UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


GIFT  OF 

Larry  Laughlin 


LEARNING  TO  FLY 

IN  THE 

U.  S.  ARMY 


LEAENING  TO  FLY 

IN  THE 

U.  S.  AKMY 

A  MANUAL  OF  AVIATION 
PRACTICE 

BY 
E.  N.  TALES 

ASSISTANT   PROFESSOR    OF    MECHANICAL   ENGINEERING 
CHAIR    OF   AERONAUTICS,    UNIVERSITY    OF   ILLINOIS 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET.    NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

6  &  8  BOUVERIE  ST.,  E    C. 

1917 


TL 


PREFACE 

The  contents  of  this  book  run  parallel  to  the  in- 
struction given  under  the  author's  direction  in  the 
U.  S.  Ground  School  of  Military  Aeronautics,  Uni- 
versity of  Illinois  branch.  In  it  are  set  forth  the 
main  principles  of  flying,  such  as  the  aviator  must 
know  in  order  to  properly  understand  his  airplane, 
keep  it  trued  up,  and  operate  it  in  cross  country 
flights  as  well  as  at  the  flying  field. 

With  the  sudden  expansion  of  the  Aviation  Sec- 
tion of  the  U.  S.  Army  since  the  declaration  of  a 
°*  state  of  war  with  Germany,  no  book  has  been  exactly 
m  suited  to  the  aeronautic  instruction  of  our  30,000 
^  aviation  students.     These  young  men,  called  from 
^  non-technical   occupations   at   short   notice,    must 
=>  cram  themselves  in  a  few  weeks  with  the  gist  of 
^  airplane  flying,  and  must  therefore  omit  everything 
except  the  outstanding  fundamentals. 

The  following  pages  set  forth  to  the  non-technical 
student  aviator  the  gist  of  aviation,  in  such  a  manner 
that  accuracy  is  not  sacrificed  to  brevity.  The 
present  book  aims  to  give  the  desired  essentials, 
omitting  many  technical  details  of  interest  to  the 
aeronautical  engineer,  to  whose  needs  other  larger 
textbooks  are  adapted  as  a  complete  survey  of 
technical  aeronautics. 

Out  of  the  2000  aeronautical  books  now  in  exist- 


345544 


Vlll  PREFACE 

ence,  a  few  are  adapted  to  use  as  textbooks  for  the 
present  need,  but  none  gives  the  particular  and 
abridged  information  in  tabloid  form  such  as  must 
be  adopted  for  the  best  time  economy  of  these 
students. 

The  chapters  on  " Rigging"  are  not  abridged  so 
much  as  are  the  other  chapters,  but  are  given  in 
some  detail;  this  is  to  fill  a  definite  need  among 
student  aviators  for  material  based  on  practical 
experience. 

In  the  chapters  on  " History  of  Aviation"  only 
those  experiments  are  treated  which  have  a  bearing 
on  flight  today;  this  chapter  is  to  be  read  in  con- 
junction with  the  chapter  on  " Principles  of  Flight" 
especially  as  regards  controlling  the  airplane. 

The  question  of  Airplane  Motors  has  not  been 
touched,  because  to  do  it  justice  would  unduly 
increase  the  size  of  this  volume,  and  because  good 
treatises  on  this  subject  are  available. 

Acknowledgment  is  due  Professor  Holbrook  and 
Messrs.  Beyer  and  Hebbard  of  the  University  of  Illi- 
nois for  the  preparation  of  Chapters  VI  to  XI. 

Aug.  16,  1917. 


CONTENTS 

PAGE 

PREFACE vi 

CHAPTER 

I.  History  of  Aviation 1 

II.  Types  of  Military  Airplanes  and  Uses 18 

III.  Principles  of  Flight 39 

IV.  Flying  the  Airplane 80 

V.  Cross-country  Flying 89 

VI.  The  Rigging  of  Airplanes — Nomenclature 113 

VII.  Materials  of  Construction 120 

VIII.  Erecting  Airplanes 133 

IX.  Truing  up  the  Fuselage 158 

X.  Handling  of  Airplanes  in  the  Field  and  at  the  Bases 

Previous  to  and  After  Flights 166 

XI.  Inspection  of  Airplanes 173 


LEARNING  TO  FLY 

IN  THE 

U.  S.  ARMY 


A  MANUAL  OF  AVIATION 
PRACTICE 


CHAPTER  I 
HISTORY  OF  AVIATION 

That  part  of  the  history  of  Aviation  which  has 
especial  interest  for  aviators  is  of  recent  date,  and 
extends  back  only  two  dozen  years.  Of  course 
efforts  have  been  made  toward  manflight  ever  since 
the  early  sixteenth  century,  when  Leonardo  da 
Vinci  invented  the  parachute  and  became  the  first 
patron  of  aeronautics;  between  the  time  of  this 
famous  artist  and  the  present  many  experimenters 
have  given  their  attention  to  the  problem,  but 
previous  to  the  last  decade  of  the  nineteenth  cen- 
tury nothing  practical  was  achieved.  Then,  with 
the  perfection  of  the  steam  engine  and  the  develop- 
ment of  the  gasoline  engine,  there  came  inducement 
to  sound  experimentation,  bringing  forth  such  well- 
known  figures  as  Maxim,  Langley,  Lillienthal  and 
Chanute. 

The  work  of  each  of  these  men  is  an  interesting 
story  by  itself,  especially  that  of  Langley,  who 
approached  the  matter  from  a  strictly  scientific 
l 


2  MANUAL  OF  AVIATION  PRACTICE 

viewpoint,  established  testing  apparatus  and  built 
successful  self-propelled  steam  models  years  before 
the  Wright  brothers  reported  their  independent 
successes.  He  reproduced  his  models  to  full  scale 
with  every  expectation  of  success,  but  failed,  due 
to  exhaustion  of  his  capital. 

Langley's  Experiments  in  Aerial  Navigation. — 
In  all  the  history  of  aerial  navigation  one  of  the 
most  romantic  stories  is  that  describing  the  scientific 
researches  begun  in  1887  by  Langley  and  culminat- 
ing in  1896  in  the  first  really  successful  case  of 
mechanical  flight  using  a  prime  mover;  continuing 
up  to  1903  when  this  first  successful  machine,  a 
model  of  12-ft.  span,  was  reproduced  to  full  scale 
and  manned  for  its  trial  flight  by  a  human  pilot ;  and 
ending  with  the  destruction  of  this  full-sized  ma- 
chine on  launching,  so  that  Langley  missed  the 
glory  of  being  the  actual  discoverer  of  manflight 
only  by  a  hair's  breadth,  dying  shortly  afterward  of 
a  broken  heart,  as  is  conceded  by  those  who  knew 
him.  If  this  full-scale  machine  had  performed  as 
successfully  in  1903  as  it  actually  did  after  being 
rebuilt  and  partly  remodelled  a  decade  later  by 
the  Curtiss  company,  Langley  would  have  antedated 
the  first  successful  flight  made  by  the  Wright 
brothers  by  a  narrow  margin  of  about  2  months. 

Lillienthal  (Germany,  1894). — But  omitting  de- 
tails regarding  the  early  experimenters  we  will 
consider  only  that  part  of  the  history  of  aviation 
most  important  to  the  prospective  aviator.  We 
will  confine  ourselves  to  the  sequence  of  gliding  and 


HISTORY  OF  AVIATION 


4  MANUAL  OF  AVIATION  PRACTICE 

power  experiments  begun  by  Lillienthal,  carried 
forward  by  Chanute  and  brought  to  completion  by 
the  Wrights. 

Lillienthal  was  the  first  man  to  accomplish  suc- 
cessful flights  through  the  air  by  the  use  of  artificial 


(Courtesy  Jas.  Means'  "Aeronautical  Annual.") 
FIG.  2. — Lillienthal's  biplane  glider  in  flight,  1894. 
Note. — (a)  Arched  wings;  (6)  fixed  tail;  (c)  method  of  balancing  by  swinging  legs 


wing  surfaces.  After  many  years  of  experiment 
and  study  of  soaring  birds  he  constructed  rigid 
wings  which  he  held  to  his  shoulders  and  which, 
after  he  had  gained  considerable  velocity  by  run- 
ning forward  downhill,  would  catch  the  air  and  lift 


HISTORY  OF  AVIATION 


his  weight  completely  off  the  ground.  The  wings 
were  arched,  for  he  observed  this  was  the  case  in 
all  birds;  flat  wings  proved  useless  in  flight,  and 
suggested  a  reason  for  the  failure  of  previous  experi- 


fctf        sJFW 

j&j 


(Courtesy  Jas.  Means'  "Aeronautical  Annual.") 

FIG.  3. — Chanute's  biplane  glider,  1896. 

Note  improvement  in  rigidity  by  bridge-type  trussing. 

menters.  To  these  rigid  wings  Lillienthal  fastened 
a  rigid  tail;  the  wings  and  the  tail  comprised  his 
"glider."  There  were  no  control  levers  and  the 
only  way  the  operator  could  steer  was  to  shift  the 
balance  by  swinging  his  legs  one  way  or  the  other. 


6  MANUAL  OF  AVIATION  PRACTICE 

Lillienthal  constructed  an  artificial  hill  for  his  glid- 
ing so  that  he  could  coast  downward  for  some  dis- 
tance without  striking  the  ground  and  he  was  able 
to  accomplish  many  glides  of  a  couple  of  hundred 
yards  in  length. 

Chanute  (Chicago,  1896). — Chanute's  experi- 
ments in  gliding  were  quite  similar  to  Lillienthal' s 
and  were  made  on  the  sand  dunes  along  Lake  Michi- 
gan outside  of  Chicago.  His  apparatus  was  more 
strongly  constructed,  being  of  trussed  biplane  type, 
a  construction  suggested  to  him  by  his  experience 
in  bridge  building,  and  one  which  persists  today  as 
the  basis  of  strength  in  our  present  military 
biplanes. 

The  Wright  Brothers,  1901.— Lillienthal  was 
killed  in  a  glide,  having  lost  control  of  his  apparatus 
while  some  distance  above  the  ground.  The  Wright 
brothers  read  of  his  death  and  commenced  thinking 
over  the  whole  problem.  LillienthaPs  method  of 
balancing  his  large  apparatus  by  the  mere  effect 
of  swinging  his  legs  appeared  to  them  as  a  very 
inadequate  means  of  control.  They  came  to  the 
conclusion  that  the  immediate  problem  in  artificial 
flight  was  the  problem  of  stability,  which  they 
felt  should  be  solved  by  an  entirely  different 
means  than  that  employed  by  Lillienthal  and 
Chanute.  The  work  already  done  had  demon- 
strated without  question  that  support  in  the  air 
had  been  established;  with  the  addition  of  control- 
lability the  Wrights  looked  forward  to  doing  some- 
thing worth  while  in  the  way  of  artificial  flight. 


HISTORY  OF  AVIATION  7 

To  improve  LillienthaFs  method  of  shifting  the 
weight,  they  conceived  the  idea  of  leaving  the  pilot 
in  an  immovable  position  in  the  glider,  and  instead 
of  obliging  him  to  shift  his  weight  this  way  and  that, 
they  proposed  to  manipulate  the  surfaces  of  the 
wings  themselves  by  means  of  levers  under  the 
pilot's  control,  so  that  the  same  result  of  balancing 
could  be  obtained  by  quite  a  different  and  superior 
method. 

They  set  out,  therefore,  deliberately  to  solve  the 
whole  question  of  airplane  stability.  There  was 
the  fore  and  aft  or  horizontal  stability,  for  which 
Lillienthal  had  swung  his  legs  forward  and  back- 
ward; there  was  in  addition  the  side  wise  or  lateral 
stability  for  which  Lillienthal  had  swung  his  legs 
to  left  and  right.  The  fundamental  requirements 
to  be  met  were  that  during  flight  the  glider  should 
be  kept  in  its  proper  attitude  without  diving  or 
rearing  up,  and  without  rolling  into  an  attitude 
where  one  wing  tip  was  higher  than  the  other,  i.e., 
the  machine  was  to  be  kept  level  in  both  directions. 

Fore  and  Aft  Control. — After  some  preliminary 
trials  the  Wrights  found  that  the  fore  and  aft 
balance  could  be  controlled  by  an  elevator  or  hori- 
zontal rudder,  supported  on  outriggers  on  the  front 
of  the  airplane,  and  operated  by  a  lever.  If  the 
pilot  found  the  glider  pitching  too  much  downward, 
and  tending  toward  a  dive,  he  would  tilt  the 
elevator  upward  by  moving  the  lever,  thus  turning 
the  glider  back  into  its  proper  attitude.  This 
elevator  in  modern  machines  is  back  of  the  airplane, 


MANUAL  OF  AVIATION  PRACTICE 


II 


HISTORY  OF  AVIATION 

a  better  place  for  it  than  was  chosen  by  the  Wrights. 
It  may  be  said  that  their  chief  reason  for  first  put- 
ting it  in  front  was  that  they  could  see  it  there  and 
observe  its  effect.  They  soon  realized  that  the 
rear  location  gave  easier  control,  and  they  acted 
accordingly. 

Lateral  Control.— After  satisfying  themselves  re- 
garding fore  and  aft  control,  the  Wrights  took  up 
lateral  control.  Their  problem  was  to  devise  a 
means  for  keeping  the  span  of  the  wings  level  so 
that  when  for  any  reason  one  wing  tip  should 
sink  lower  than  the  other,  it  could  be  at  once  raised 
back  to  its  proper  position.  Lillienthal  had  tried 
to  do  this  by  swinging  his  legs  toward  the  high  side ; 
the  shifted  weight  restoring  the  position.  The 
Wrights,  to  obviate  this  inadequate  method,  be- 
thought themselves  to  restore  equilibrium  by  means 
of  the  wind  itself  rather  than  by  gravity.  They 
observed  an  interesting  maneuver  employed  by  a 
pigeon  which  seemed  to  secure  its  lateral  balance 
in  exactly  the  way  they  wanted;  this  bird  was  seen 
to  give  its  two  wings  each  a  different  angle  of  attack, 
whereat  one  wing  would  lift  more  forcibly  than  the 
other,  thereby  rotating  the  bird  bodily  in  any 
desired  amount  or  direction  about  the  line  of  flight 
as  an  axis.  To  copy  this  bird  apparatus  in  a  Wright 
glider,  it  was  found  sufficient  to  alter  the  angle  of 
the  wing  tips  only,  leaving  the  chief  part  of  the 
supporting  surface  in  its  original  rigid  position. 
In  other  words,  the  wing  tips  were  to  be  warped; 
the  one  to  present  greater  angle  of  attack,  the  other 


10  MANUAL  OF  AVIATION  PRACTICE 

less  angle,  exactly  as  in  the  case  of  the  pigeon. 
Suppose  the  airplane  to  develop  a  list  to  the  left, 
the  wing  on  that  side  sinking,  the  pilot  was  to  in- 
crease the  angle  at  the  tip  of  this  left-hand  wing  by 
moving  the  warping  lever,  and  at  the  same  time 
decrease  the  angle  of  the  right-hand  wing  by  the 
same  lever.  He  was  to  hold  this  position  until  the 
airplane  was  righted  and  brought  back  to  level 
position. 

This  arrangement  proved  to  have  the  effect 
anticipated  and  maintained  stability  easily  on  a 
glider  much  larger  than  Lillienthal  ever  managed 
with  his  leg-swinging  method. 

Directional  Control. — We  have  now  followed  the 
development  by  the  Wrights  of  airplane  control 
as  regards : 

1.  Fore  and  aft  or  "pitching"  motion,  accom- 
plished by  an  elevator  operated  by  lever. 

2.  Lateral  or  " rolling"  motion  accomplished  by 
wing  warping  operated  by  a  second  lever. 

These  were  the  only  controls  used  in  the  earliest 
gliders.  It  remains  to  consider  the  third  element 
of  control,  viz : 

3.  The  directional  or  " yawing"  control,  which  is 
accomplished  by  an  ordinary  vertical  rudder  oper- 
ated by  a  third  lever. 

The  Wrights  found  the  warping  had  all  the  effect 
anticipated  but  had  also  certain  secondary  and 
undesirable  effects.  Whenever  they  applied  the 
warping  lever  to  correct  the  rolling  motion,  the 
glider  responded  as  far  as  rolling  control  was 


HISTORY  OF  AVIATION  11 

concerned,  but  at  the  same  time  would  "yaw"  or 
swerve  out  of  its  course  to  right  or  left.  This  was 
a  serious  complication.  For,  in  the  moment  of 
swerving,  the  high  wing  which  they  desired  to 
depress  would  advance  faster  than  the  low  wing,  and 
solely  by  its  higher  velocity  tended  to  develop  a 
greater  lift  and  thereby  neutralize  the  beneficial 
effect  of  the  warp.  In  many  of  their  early  glides, 
because  of  pronounced  swerving,  the  warp  effect 
was  entirely  counteracted  and  failed  to  bring  the 
glider  back  to  level;  with  the  result  that  one  wing 
tip  would  sink,  at  the  same  time  swinging  backward 
until  the  machine  was  brought  to  the  ground. 
No  amount  of  controlling  could  prevent  this. 

After  much  bewilderment  on  this  point,  the 
Wrights  observed  that  whenever  a  wing  tip  was 
warped  to  a  large  angle  its  resistance  became 
relatively  greater  and  it  slowed  up  while  the  oppo- 
site side  went  ahead.  They  at  once  hit  upon  the 
idea  of  a  rudder,  previously  considered  unnecessary, 
which  they  believed  could  be  turned  in  each  case 
of  yawing  just  enough  to  create  a  new  and  apposing 
yawing  force  of  equal  magnitude. 

They  therefore  attached  a  rudder  at  the  rear, 
connecting  its  tiller  ropes  to  lever  No.  2,  and  giving 
this  lever  a  compound  motion  so  that  one  hand  could 
operate  either  warp  or  rudder  control  independently 
(or  simultaneously  in  proper  proportion  to  eliminate 
the  yawing  tendency  above  mentioned).  This 
combination  is  the  basis  of  the  Wright  patents  and 
is  essential  in  airplanes  of  today. 


12  MANUAL  OF  AVIATION  PRACTICE 

Great  success  now  ensued  in  their  gliding  experi- 
ments; the  machine  was  always  in  perfect  control; 
could  be  manipulated  in  any  desired  manner;  turned 
to  right  or  left,  or  brought  down  to  earth  with  safety. 

Thus  were  the  three  elements  of  control  applied 
by  the  Wrights  to  their  glider  and  the  problem 
apparent  in  Lillienthal's  death  was  solved.  The 
next  step  was  to  install  a  power  plant  able  to  main- 
tain forward  speed  without  resorting  to  coasting 
downhill  by  gravity;  and  therefore  capable  of  pro- 
ducing a  horizontal  flight. 

In  developing  a  power  flyer  aside  from  the  ques- 
tion of  control  the  proper  design  was  arrived  at  as 
follows : 

Efficiency  of  Wings. — The  Wrights  knew  from 
Langley  and  Chanute  that  flat  wings  were  inefficient 
and  useless,  and  curved  wings  essential;  they  did  not 
know  whether  the  amount  of  curvature  mattered 
much.  To  find  this  out  by  trials  in  gliding  would 
be  slow  and  expensive.  They  adopted  a  better 
way — the  wind-tunnel  method,  wherein  small- 
scale  models  were  tested  and  compared  for  efficiency 
in  a  blast  of  air.  They  made  their  wind  tunnel  16 
in.  in  diameter  and  created  a  powerful  air  blast 
through  it  by  means  of  an  engine-driven  fan.  Small 
models  of  wings  were  placed  in  the  center  of  this 
confined  air  blast,  mounted  on  a  balance  arm  which 
projected  into  the  tunnel  from  the  outside.  The  air 
forces  and  efficiency  of  the  models  were  thus  meas- 
ured. A  large  variety  of  shapes  were  tested  and 
one  was  selected  as  best  of  all  from  the  standpoint 


HISTORY  OF  AVIATION  13 

of  curvature  and  rounded  wing  tips.  This  shape 
was  adopted  in  their  flyer,  and  though  on  a  much 
larger  scale  fulfilled  the  predictions  made  for  its 
efficiency  in  the  indoor  wind-tunnel  experiments. 

The  Wright  glider  was,  of  course,  a  biplane  model. 
They  tested  a  small  6-in.  model  biplane  and  found 
that  the  two  wings  together  were  less  efficient  than 
either  wing  by  itself.  However,  other  considera- 
tions, such  as  rigidity  of  trussing,  decided  them  to 
adopt  the  biplane  rather  than  a  monoplane 
arrangement. 

Low  Resistance  to  Forward  Motion. — The 
Wrights  used  their  wind  tunnel  also  in  choosing  for 
the  struts  of  their  airplane  a  shape  which  would 
present  least  head  resistance  to  forward  motion. 
They  found  that  a  square  strut  had  a  resistance 
which  could  be  decreased  by  changing  the  shape  to 
resemble  a  fish.  The  resistance  of  the  pilot  him- 
self was  decreased  by  making  him  lie  prone,  face 
downward  on  the  bottom  wing. 

Propeller  Efficiency. — Although  little  data  on  the 
subject  of  propeller  efficiency  was  available  to  the 
Wrights,  they  were  able  to  arrive  at  a  very  credit- 
able design  wherein  two  propellers  were  used, 
driven  from  a  single  motor,  and  rotating  one  each 
side  of  the  pilot.  The  mechanical  difficulties  which 
have  since  embarrassed  the  use  of  two  propellers 
were  less  with  the  Wrights  because  they  were  deal- 
ing with  smaller  horsepowers  than  are  in  use  today ; 
they  therefore  were  able  to  realize  a  very  high  pro- 
peller efficiency. 


14  MANUAL  OF  AVIATION  PRACTICE 

Motor. — When  the  Wrights  were  ready  to  apply 
a  motor  to  their  glider,  they  found  it  impossible 
to  secure  one  light  enough,  and  had  to  set  about 
building  one  themselves.  They  adopted  a  four- 
cylinder  type,  water-cooled,  and  their  aim  was  to 
save  weight  and  complication  wherever  possible. 
Then-  first  motor  gave  about  12  hp.,  which  was 
raised  to  a  higher  and  higher  figure  by  subsequent 
improvements  until  it  reached  20  hp.  In  its 
earliest  stages  it  was  able  to  give  sufficient  power 
for  short  horizontal  flights. 

Means  of  Starting  and  Landing. — One  reason  the 
Wrights  could  use  such  low  horsepower  was  that 
they  employed  auxiliary  starting  apparatus  to  get 
up  original  speed.  They  knew  that  less  horsepower 
was  necessary  to  fly  an  airplane  after  it  was  once  in 
the  air  than  was  necessary  to  get  it  into  the  air  at 
the  start,  and  they  therefore  rigged  up  a  catapult 
which  projected  their  airplane  forward  on  a  rolling 
carriage  with  great  force  at  the  start,  so  that  all  the 
motor  had  to  do  was  to  maintain  the  flight  in  air. 
The  Wright  airplane  had  at  first  no  landing  wheels, 
and  was  provided  only  with  light  skids  on  which  it 
could  make  a  decent  landing.  Present-day  air- 
planes, of  course,  have  wheels  on  which  to  roll  both 
at  starting  and  at  landing  and  their  motors  are 
powerful  enough  to  eliminate  the  necessity  for  a 
starting  catapult. 

Bleriot's  Contribution  to  Aviation. — Bleriot  ex- 
perimented a  great  many  years  before  he  attained 
success  and  did  so  years  after  the  Wrights  had 


HISTORY  OF  AVIATION 


15 


SIDE    ELEYA7-/ON 


FRO/iT    EL£YAT/ON 


(Courtesy  American  Technical  Society  and  Scientific  American  Supplement.) 
FIG.  5. — Details  of  Bleriot  XI  monoplane. 


16  MANUAL  OF  AVIATION  PRACTICE 

successfully  flown.  But  when  he  did  obtain  success, 
his  great  ingenuity  produced  features  of  design 
which  were  a  decided  step  forward.  He  added  a 
body  to  the  airplane  and  produced  a  machine  which 
instead  of  being  a  pair  of  wings  with  various  append- 
ages, was  a  body  to  wThich  wings  were  attached, 
giving  a  more  shipshape  and  convenient  arrange- 
ment. The  motor,  instead  of  being  located  beside 
the  pilot  as  in  the  Wright  machine,  was  put  in  the 
very  front  of  the  body  ahead  of  the  pilot  where  it 
was  not  likely  to  fall  on  him  in  case  of  a  smash. 
This  location  of  the  motor  entailed  the  use  of  a 
single  propeller  at  the  front,  a  " tractor"  screw  as  it 
was  called,  less  efficient  than  the  double  propeller 
of  the  Wrights,  but  better  from  the  standpoint  of 
mechanical  convenience.  The  body  of  a  Bleriot, 
which  was  quite  similar  to  the  body  of  any  bird  in 
its  general  arrangement,  projected  to  the  rear  in  a 
tapering  form  and  carried  at  the  rear  a  rudder  and 
elevator.  The  motor,  pilot  and  tanks  were  thus 
enclosed  within  the  body  and  away  from  the  wind. 
Bleriot's  contributions  were  then,  better  location  of 
the  motor,  adaptation  of  the  body  or  " fuselage," 
elimination  of  the  front  elevator  and  substitution  of 
the  rear  elevator. 

Nieuport  and  Fokker's  Contribution  to  Aviation. 
— A  further  advance  on  Bleriot's  design  was  made 
by  Nieuport  and  later  by  Fokker.  The  former 
utilized  the  fuselage  principle  of  Bleriot  and  en- 
closed the  whole  framework,  front  and  back,  to 
give  a  stream-line  form,  and  even  went  so  far  as  to 


HISTORY  OF  AVIATION 


17 


make  wind-tunnel  experiments  from  which  he  was 
able  to  choose  a  very  efficient  fuselage  shape  as  well 
as  wing  and  strut  efficiency. 


(From  Hayward's  "Practical  Aeronautics.") 
FIG.  6. — Nieuport  monoplane. 
Representing  an  advance  in  speed,  due  to  covered  streamline  body. 


CHAPTER  II 

TYPES  OF  MILITARY  AIRPLANES  AND  THEIR 
USES 

Modern  Airplanes  Combining  Best  Features  of 
Previous  Experiments. — The  modern  airplane,  of 
which  the  Curtiss  training  machine  used  at  the 
U.  S.  Aviation  Schools  is  typical,  is  a  combination 
of  the  best  features  referred  to  above.  It  is  of  the 
biplane  type  for,  as  shown  by  Chanute,  rigid  truss- 
ing is  thus  possible,  an  advantage  sufficient  to  offset 
the  slight  loss  of  efficiency  which  exists  in  the  biplane. 
The  landing  gear  consists  of  two  wheels  provided 
with  shock  absorbers;  the  body  is  of  the  general 
stream-line  type,  enclosed  from  front  to  back, 
containing  comfortable  seats  for  the  passengers  and 
enclosing  the  motor  and  tanks  away  from  the  wind. 
The  motor  is  at  the  front  where,  in  an  accident,  it 
will  not  be  on  top  of  the  pilot.  The  warping  effect 
is  obtained  by  hinging  flaps  at  the  wing  tips,  the 
same  effect  being  obtained  while  at  the  same  time 
leaving  the  whole  wing  structure  rigid  and  strong 
rather  than  flexible  and  weak,  as  was  the  case  in 
the  early  warping  type  of  machines. 

Military  Airplanes  of  Today. — In  the  modern 
airplane,  therefore,  we  see  that  matters  of  efficiency, 
to  which  the  Wrights  gave  great  attention,  have 

18 


TYPES  OF  MILITARY  AIRPLANES  19 

been  sacrificed  in  favor  of  convenience,  particularly 
in  favor  of  power  and  speed.  This  is  the  effect  of 
military  demands  for  airplanes  where  power,  speed, 
and  ability  to  climb  fast  are  vital  requirements. 
To  escape  from  or  to  destroy  an  enemy,  high  speed 
and  ability  to  climb  fast  are,  of  course,  prerequisites. 
Moreover,  from  the  standpoint  of  safety  in  man- 
euvering it  is  desirable  to  have  a  reserve  of  power  and 
speed.  Therefore,  the  design  of  military  machines 
has  tended  in  a  given  direction  up  to  the  present. 

New  considerations  have  arisen  on  this  account, 
such  as  for  instance  the  question  of  landing.  Fast 
machines  in  general  make  high-speed  landings,  and 
are  for  that  reason  dangerous.  The  original  Wright 
machines  were  built  to  land  at  such  a  slow  speed 
that  ordinary  skids  were  sufficient  to  take  the  shocks. 
Nowadays  the  high-powered  airplane  is  likely  to 
come  to  grief  in  landing  more  than  at  any  other 
time.  The  question  of  stability  in  flight  has  of 
recent  years  been  treated  mathematically  and 
experimentally,  using  of  course  the  fundamental 
system  of  " three  axes  control"  first  applied  by  the 
Wrights.  It  has  been  found  that  by  properly  pro- 
portioning the  tail  surfaces  and  properly  arranging 
the  wings  and  center  of  gravity,  any  desired  degree 
of  stability  may  be  obtained,  such  that  a  machine 
may  be  made  almost  self-flying  or,  if  preferred, 
may  be  made  very  sensitive. 

All  of  the  above  features  of  design  have  had  con- 
sideration in  the  latest  types  of  military  airplanes. 
Observe  the  high  speed  of  the  latest  speed  scouts, 


20  MANUAL  OF  AVIATION  PRACTICE 

where  power  is  concentrated  exclusively  on  speed 
and  climbing  ability  and  landing  speed  is  danger- 
ously high.  We  see  the  advent  of  the  triplane  scout, 
which  is  an  attempt  to  secure  slow  landing  speed 
combined  with  high  flying  speed.  We  see  machines 
with  the  motor  and  propeller  in  the  rear,  or  with 
two  motors,  one  to  each  side  of  the  body  out  in 
the  wings,  the  object  being  to  avoid  interference  of 
the  propeller  with  the  range  of  gun  fire.  In  short, 
we  see  the  effect  of  many  military  considerations 
on  the  design  of  the  airplane.  It  will  be  interesting 
at  this  point  to  survey  what  are  these  military  uses 
of  the  airplane. 

Aerial  Fighting. — Fighting  in  the  air  is  the  most 
spectacular  use  to  which  military  airplanes  have 
been  put.  The  first  requirements  in  a  fighting 
airplane  are  speed  and  climbing  ability  and  these 
must  be  obtained  at  all  costs,  because  speed  and 
climb  are  weapons  of  defense  and  offense  second 
only  in  value  to  the  gun  itself.  The  concentration 
of  motive  power  for  speed  and  climb  requires  that 
as  little  weight  as  possible  be  used;  and  therefore 
the  fastest  fighters  are  designed  to  carry  only  one 
person  and  are  very  light  and  of  course  very  small. 
It  is  usual  to  have  one  gun  fixed  to  the  body  and 
firing  through  the  propeller  in  the  case  of  a  tractor, 
and  a  second  adjustable  aim  gun  pointing  upwards 
over  the  top  wing.  This  gives  the  pilot  a  chance  to 
fire  a  round  at  the  enemy  while  " sitting  on  his  tail" 
or  following  from  behind;  and  then  when  diving 
below  the  enemy^the  second  gun  is  available  for 


TYPES  OF  MILITARY  AIRPLANES  21 

shooting  overhead.  These  very  high-speed  fighters 
are  difficult  to  land,  due  to  their  speed,  and  are 
suitable  only  for  the  highest-trained  pilots. 

Directing  Artillery  Fire. — The  friendly  airplane 
is  sent  out  over  the  enemy's  positions,  soars  above 
the  target,  sends  back  signals  by  wireless  to  the 
friendly  battery  regarding  the  effect  of  fire;  prac- 
tically dictating  the  success  of  artillery  operations. 

Reconnaissance. — The  friendly  airplanes  go  out, 
usually  in  squads  for  the  sake  of  protection,  and 
observe  by  means  of  photographs  or  vision  size  of 
enemy  troops,  batteries,  trenches,  lines  of  com- 
munication, etc.;  report  the  situation  to  head- 
quarters as  a  source  of  daily  photographic  record 
of  the  operations  of  the  enemy,  to  such  an  extent 
that  any  change  of  the  enemy's  position  can  be 
analyzed.  Of  course  the  value  of  reconnaissance  is 
lessened  when  the  enemy  disguises  his  gun  em- 
placements, etc.  In  reconnaissance  machines  it  is 
important  to  have  two  persons,  one  to  steer  and 
the  other  to  scan  the  countryside.  The  recon- 
naissance machine  is  therefore  a  two-place  type 
which  may  or  may  not  have  armament.  It  need 
not  be  so  fast,  especially  when  convoyed  by  fighting 
speed  scouts.  The  two-place  machines  are  fre- 
quently used  for  fighting,  in  which  case  the  pilot 
will  have  a  gun  fixed  to  the  body  and  shooting 
through  the  propeller,  and  the  passenger,  especially 
in  German  machines,  will  also  have  a  gun  mounted 
in  the  turret  so  that  it  may  be  shot  in  a  variety  of 
directions  by  the  passenger. 


22  MANUAL  OF  AVIATION  PRACTICE 

Bomb  Dropping. — This  maneuver  requires  squad 
flights  to  be  of  great  value.  The  fundamental 
characteristic  of  a  bombing  airplane  is  its  ability 
to  carry  great  weight.  Such  machines  are  of 
comparatively  large  size  and  not  particularly  fast. 
Weight  carrying  is  of  course  incompatible  with 
speed  and  climbing  ability  and  therefore  the 
bombing  machine  must  be  a  compromise  if  it  is 
to  have  any  reasonable  speed.  It  may  be  said  that 
airplanes  compare  very  unfavorably  with  dirigible 
balloons  for  bomb  raids  because  the  latter  are  able 
to  carry  several  tons  of  bombs  as  against  the 
airplane's  quarter  of  a  ton. 

Locating  Submarines. — For  coast  patrol  or  sub- 
marine spotting,  the  airplane  is  an  important  factor, 
for  from  an  airplane  it  is  possible  to  see  for  a  con- 
siderable depth  into  the  water,  and  to  locate  hostile 
submarines. 

Training  Student  Aviators. — The  training  ma- 
chine on  which  prospective  aviators  secure  their 
flying  instruction  may  be  considered  as  a  type  in 
which  great  speed  and  power  is  not  essential,  but  in 
which  reliability  and  ease  of  control  is  desirable.  The 
typical  military  training  airplane  in  this  country  is  a 
single-motor  tractor  of  moderate  horsepower  (about 
100)  having  of  course  the  seats  in  tandem  and 
funished  with  dual  control  so  that  operation  may  be 
from  either  pilot's  or  passenger's  seat.  The  dual- 
control  system  of  training  which  prevails  in  this 
country  differs  from  the  French  method  of  starting 
the  pupil  out  alone  to  try  his  wings;  it  enables  the 


TYPES  OF  MILITARY  AIRPLANES 


23 


pilot  to  keep  a  constant  eye  upon  the  pupil's  con- 
trol manipulations  and  to  correct  them  instantly 
whenever  they  are  in  error  before  any  damage  is 
done.  A  possible  improvement  in  the  dual-control 
training  machine  will  be  the  substitution  of  side  by 
side  seats  for  tandem  seats.  At  present,  communi- 
cation is  difficult  due  to  the  great  noise  of  the  motor; 


FIG.  7. — U.  S.  training  airplane,  dual  control  (Curtiss  JN4). 

Speed  43  to  72  mi.  per  hr. ;  climbing  ability  300  ft.  per  min.;  90  h.p. ;  weignt 

fully  loaded  1,890  Ibs. 


but  with  the  adoption  of  side  by  side  seats  such  as  is 
used  in  naval  training  schools,  the  pilot  and  pupil 
will  be  able  to  communicate  to  better  advantage. 

Types  of  Airplanes. — To  suit  the  foregoing  pur- 
poses flying  machines  exist  in  seven  distinct  different 
shapes  at  the  present  time,  namely :  monoplanes,  bi- 
planes, triplanes,  single-motor  tractors,  single-motor 
pushers,  double-motor  machines  and  marine  air- 
planes. The  last  four  types  may  be  either  mono- 
planes, biplanes  or  triplanes.  In  order  to  under- 


24  MANUAL  OF  AVIATION  PRACTICE 

stand  the  adoption  of  one  or  the  other  type  for 
military  use,  it  is  well  to  run  over  the  characteristics 
of  the  seven  types  mentioned. 

Monoplanes. — The  simplest  form  of  airplane  is  the 
monoplane  which  is  fashioned  after  the  manner  of  a 
bird  (see  Fig.  34).  There  are  two  things  to  say  in 
favor  of  the  monoplane:  first,  that  the  passengers 
have  an  unobstructed  view  forward  and  range  of  gun 
fire  upward  because  there  is  no  wing  above  them; 
second,  the  aerodynamic  efficiency  of  the  monoplane 
is  superior  to  any  other  type.  But  when  the  bird 
design  is  applied  to  a  man-carrying  apparatus,  it 
becomes  impracticable  to  construct  spars  to  take  the 
place  of  the  bird's  wing  bones;  and  therefore  to  give 
the  wings  proper  strength  it  becomes  necessary  to 
truss  them  with  numerous  tension  wires  stretching 
from  the  running  gear  out  to  various  portions  of  the 
wings.  There  are  also  wires  running  from  a  vertical 
mast  above  the  body  to  a  point  on  the  top  part  of  the 
wing;  these  wires,  while  they  give  the  wing  no  added 
strength  during  a  flight,  are  necessary  in  order  that 
the  shock  of  landing  shall  not  break  the  wings  off 
sharp  at  the  shoulder.  It  is  characteristic  of  mono- 
plane construction  that  from  a  point  below  the 
body  and  also  from  a  point  above  the  body  a  num- 
ber of  heavy  wires  run  outward  to  various  points  on 
the  wings;  and  it  may  be  said  that  the  strength  to  be 
secured  from  this  construction  is  not  all  that  could 
be  desired. 

Biplanes. — The  biplane  is  an  improvement  over 
the  monoplane  from  the  latter  standpoint;  in  the 


TYPES  OF  MILITARY  AIRPLANES  25 

biplane  there  are  two  parallel  surfaces  separated  by 
vertical  sticks  or  struts,  thus  forming  parallelograms 
which  are  susceptible  of  being  trussed  by  means  of 
tension-wire  diagonals  in  a  manner  familiar  and  well 
understood  in  case  of  bridges.  It  is  possible  to 
build  up  biplane  wings  of  great  rigidity  and  strength 
by  this  system,  much  more  easily  than  in  case  of 
monoplanes.  However,  the  biplane  type  is  from  the 
standpoint  of  efficiency  inferior  to  the  monoplane. 
This  is  due  to  the  fact  that  the  vacuum  above  the 
bottom  wing  which  is  so  necessary  for  high  duty  is 
somewhat  interfered  with  by  the  upper  wing;  thus 
while  in  a  biplane  the  upper  wing  operates  about  as 
efficiently  as  it  would  operate  in  a  monoplane,  yet 
the  lower  wing  has  its  efficiency  materially  reduced 
and  the  resulting  overall  efficiency  of  a  biplane  com- 
pared area  for  area  with  the  monoplane  is  about  85 
per  cent,  as  great.  However,  recent  developments 
of  the  airplane  have  more  or  less  put  efficiency  in  the 
background  and  as  a  result  today  the  biplane  is  more 
popular  than  the  monoplane.  In  addition  to  the 
greater  strength  of  biplane  wings  their  span  may  be 
less  than  the  monoplane  for  the  same  supporting 
area.  This  makes  them  less  unwieldy.  Moreover, 
for  certain  reasons  a  biplane  machine  of  high  speed 
may  be  landed  at  a  lower  speed  than  equivalent 
monoplanes. 

Triplanes. — What  is  true  of  the  biplane  is  more 
true  in  almost  every  item  of  the  triplane,  that  is,  it 
is  comparatively  strong,  compact,  and  of  low  land- 
ing speed,  but  of  reduced  efficiency. 


26 


MANUAL  OF  AVIATION  PRACTICE 


TYPES  OF  MILITARY  AIRPLANES  21 

Single -Motor  Tractors. — The  single-motor  tractor 
received  its  name  simply  because  the  propeller  is 
in  front  and  draws  the  machine  forward;  but  this 
location  of  the  propeller  necessitates  a  distinct  type 
of  airplane,  wherein  the  power  plant  is  located  at  the 
very  nose  of  the  machine.  The  tractor  type  has  the 
pilot  and  passenger  located  in  or  to  the  rear  of  the 
wings  in  order  that  their  weight  may  balance  the 
weight  of  the  motor.  This  means  that  the  view  and 
range  of  fire  of  the  passengers  is  obstructed  in  a  for- 
ward direction  by  the  wings,  and  in  machines  such 
as  the  II.  S.  training  machine,  the  passenger,  who  is 
practically  in  the  center  of  the  wings,  can  not  look 
directly  upward  nor  directly  downward.  Moreover, 
as  concerns  gun  fire,  the  propeller  of  a  ^tractor 
obstructs  the  range  straight  ahead.  In  the  tractor 
the  tail  is  supported  at  the  rear  and  on  the  same 
body  which  contains  the  motor  and  passengers;  this 
body  constitutes  a  stream-line  housing  for  the 
machinery,  seats,  etc.,  and  therefore  has  low  wind 
resistance.  The  tractor  is  a  very  shipshape  design, 
compact  and  simple  and  is  at  present  the  prevailing 
type  on  the  European  war  front.  However,  it  has 
disadvantages  which  are  only  overcome  in  other 
types.  One  of  these  disadvantages  is  of  course  the 
obstruction  to  range  of  gun  fire.  The  present 
practice  in  fighting  airplanes  is  simply  to  shoot  the 
gun  straight  through  the  circle  of  rotation  of  the  pro- 
peller on  the  assumption  that  most  of  the  bullets 
will  get  through  and  that  those  which  hit  the  shank 
of  the  propeller  blade  will  be  deflected  by  proper 


28 


MANUAL  OF  AVIATION  PRACTICE 


TYPES  OF  MILITARY  AIRPLANES 


29 


armoring.  An  attempt  is  made  to  insure  that  all  the 
shots  will  get  through  by  connecting  the  gun  mechan- 
ism mechanically  to  the  motor  shaft  in  such  a  way 
that  bullets  will  be  discharged  only  at  the  instant 
when  their  path  is  unobstructed  by  a  propeller 
blade.  This  practice  is  possible  of  course  only  in 
guns  which  are  fixed  immovably  to  the  airplane. 

Single-motor    Pusher    Airplanes. — The    pusher 
type  has  popularity  because  the  propeller  and  motor 


FIG.  10. — An  American  pusher  biplane  design. 
Crew  in  front,  motor  and  propeller  in  the  rear,  tail  support  on  outriggers. 

rotate  to  the  rear  of  the  passenger,  who  takes  his 
place  in  the  very  front  of  the  body  and  has  an  open 
range  of  vision  and  gun  fire  downward,  upward  and 
sideways.  Another  point  in  favor  of  the  pusher  is 
that  the  oil  and  fumes  of  the  motor  do  not  blow  into 
his  face  as  in  the  case  of  the  tractor.  The  disad- 
vantage of  the  pusher  is  that  the  motor,  being  lo- 
cated behind  the  pilot,  will  be  on  top  of  him  in  the 


30  MANUAL  OF  AVIATION  PRACTICE 

case  of  a  fall.  Another  disadvantage  is  that  the 
body  can  not  be  given  its  shipshape  stream-line  form 
because  to  do  so  will  interfere  with  the  rotation 
of  the  propeller.  Therefore,  the  body  is  abruptly 
terminated  just  to  the  rear  of  the  wings  and  it  is 
just  long  enough  to  hold  the  passenger  and  the 
motor,  the  propeller  sticking  out  behind.  The 
tail  surfaces  are  then  attached  to  the  airplane  by 
means  of  long  outriggers  springing  from  the  wing 
beams  at  points  sufficiently  far  from  the  propeller 
axis  so  as  not  to  interfere  with  the  propeller. 

Double -motor  Machines. — In  order  to  combine 
the  advantages  of  the  tractor  and  pusher  types  and 


FIG.  11. — U.  S.  army  battle  plane. 
Two  100  h.p.  motors;  speed  85  mi.  per  hr. 

eliminate  their  disadvantages,  the  double-motor  ma- 
chines have  been  developed.  In  these  there  is  no 
machinery  whatever  in  the  body  either  in  front  or 
back,  and  the  passengers  may  take  seats  at  the  ex- 
treme front  as  is  desirable.  The  body  then  tapers 
off  to  the  rear  in  stream-line  form  and  supports  the 
tail  surfaces.  The  power  plants  are  in  duplicate 
and  one  is  located  to  each  side  of  the  body  out  on 
the  wings.  It  is  customary  to  enclose  each  of 


TYPES  OF  MILITARY  AIRPLANES  31 

these  two  motors  in  a  casing  so  that  the  whole 
power  plant  presents  a  more  or  less  stream-line 
shape  to  the  wind,  the  propellers  projecting  from 
the  front  or  rear  of  these  stream-line  shapes.  It  may 
be  said  that  in  the  double-motor  airplane  it  makes 
very  little  difference  whether  the  propeller  is  in 
front  or  behind  so  that  while  a  " twin-motor"  ma- 
chine may  be  more  accurately  specified  as  a  "  twin- 
motor  pusher"  or  a  "twin-motor  tractor,"  it  is 
usually  sufficient  indication  of  a  machine's  charac- 
teristics to  call  it  a  twin-motor  machine. 

By  adopting  this  twin-motor  form  we  bring  in  new 
disadvantages.  One  of  these  is  due  to  the  fact  that 
the  heavy  motors  are  now  located  some  distance 
from  the  center  of  gravity  of  the  machine.  This 
requires  stronger  supporting  members  between  the 
motor  and  the  body.  It  also  makes  the  lateral  con- 
trol comparatively  logy  for  now  the  heavy  masses 
are  far  from  the  center  of  gravity,  resisting  the 
pilot's  efforts  to  use  the  lateral  control.  The  second 
disadvantage  in  the  twin-motor  type  results  from 
possible  stoppage  of  either  motor.  In  this  case,  of 
course,  the  propelling  force  is  some  distance  off 
center  and  is  also  reduced  to  one-half  its  value  re- 
quiring energetic  exercise  of  the  control  wheel  to 
maintain  equilibrium.  It  is  reported,  however,  that 
twin  machines  can  continue  to  fly  and  even  climb 
with  only  one  motor  running.  In  this  country  the 
twin-motor  type  has  not  developed  as  was  hoped  at 
first,  and  on  the  European  firing  lines  it  is  not  so 
numerous  as  the  single-motor  tractor  type. 


32  MANUAL  OF  AVIATION  PRACTICE 

Marine  Airplanes. — The  possibility  of  mechanical 
flight  having  once  been  established  and  wheels  hav- 
ing been  applied  to  the  airplane  so  that  it  could  start 
from  and  land  on  the  ground,  the  logical  next  step 
was  to  substitute  some  form  of  boat  for  the  wheels  so 
that  flights  could  be  made  over  the  water. 

Experiments  were  made  in  France  by  M.  Fabre  in 
this  direction  and  in  this  country  by  G.  H.  Curtiss. 
The  latter,  in  his  flight  down  the  Hudson  from  Al- 
bany to  New  York,  equipped  his  airplane  with  a 
light  float  to  provide  against  forced  landing  in  the 
river.  Pursuing  this  general  idea  he  made  some  ex- 
periments under  the  auspices  of  Alexander  Graham 
Bell's  Aerial  Experiment  Association,  in  which  a 
canoe  was  substituted  for  the  wheels,  and  in  which 
an  attempt  was  made  to  start  from  the  surface  of 
the  water.  Success  did  not  come  at  first  and  this 
plan  gave  no  satisfaction.  Curtiss  next  turned  his 
attention  to  the  hydroplane  type  of  boat  and  made 
a  series  of  experiments  at  San  Diego.  The  hydro- 
plane appeared  to  be  much  better  adapted  to  his 
purpose  than  the  canoe  had  been,  and  he  was  able 
to  obtain  success. 

The  Hydro -airplane  (or  "Seaplane").— From 
analogy  to  the  airplane  one  might  at  first  imagine 
that  a  suitable  hydroplane  would  have  a  wide  span 
and  fore  and  aft  length;  but  such  proportion  would 
give  a  very  poor  stability  on  the  water,  and  would 
require  auxiliary  hydroplanes  in  the  same  way  that 
an  airplane  requires  auxiliary  guiding  surfaces.  So 
Curtiss,  with  his  customary  eye  for  simplicity  and 


TYPES  OF  MILITARY  AIRPLANES 


33 


34 


MANUAL  OF  AVIATION  PRACTICE 


TYPES  OF  MILITARY  AIRPLANES  35 

convenience,  adopted  a  type  of  hydroplane  which 
had  the  general  proportions  of  an  ordinary  boat, 
i.e.,  was  long  and  narrow,  thus  obviating  the  neces- 
sity of  auxiliary  hydroplanes  at  the  tail  of  the  ma- 
chine. To  prevent  the  machine's  tipping  over 
side  wise,  "wing  pontoons"  were  attached  at  the 
lower  wing  tips  to  prevent  capsizing. 


FIG.  14. — Building  a  flying  boat  hull. 
Note  wing  stumps  and  hydroplane  fins. 

The  Flying  Boat. — In  the  early  hydro-airplane, 
which  was  thus  developed,  the  motor  and  pilot  were 
above  in  the  usual  position  in  the  wings,  while  the 
hydroplane  itself  was  a  considerable  distance  below 
the  wings.  Thus  there  was  a  good  ,deal  of  head 
resistance.  Curtiss  set  about  reducing  this  head 
resistance  as  far  as  possible  and  tried  to  incorporate 
the  pilot's  seat  with  the  hydroplane  pontoon.  The 
outcome  of  his  endeavor  was  that  he  developed  a 
boat  with  a  tapering  stern.  The  pilot,  gasoline 


36 


MANUAL  OF  AVIATION  PRACTICE 


tanks,  etc.,  are  located  inside  of  the  hull;  the  tapering 
stern  provides  a  backbone  to  which  the  tail  sur- 
faces can  be  readily  attached;  the  wings  fixed  to  the 
sides  of  the  hull  in  a  manner  analogous  to  the  wing 
fastenings  of  the  modern  military  airplane;  and  the 
motor  alone  remains  exposed  to  the  wind.  This  is 
the  flying  boat ;  its  action  on  the  water  is  analogous 


FIG.   15. — Method  of  hoisting  a  marine  airplane  aboard  ship. 

to  the  action  of  the  hydroplane  for  the  bottom  of 
this  boat  hull  is  made  in  hydroplane  form;  indeed, 
in  the  latest  types  of  flying  boat,  the  hydroplane 
area  is  increased  by  extending  it  to  right  and  left 
of  the  boat  hull.  The  flying  boat  is  an  ingenious 
combination,  wherein  the  characteristics  of  the 
hydroplane  are  combined  with  the  seaworthiness 
of  the  ordinary  boat,  and  at  the  same  time  wind 
resistance  is  reduced  to  a  minimum. 


TYPES  OF  MILITARY  AIRPLANES  37 

The  hydro-airplane  remains  in  use,  however, 
being  preferable  to  the  flying  boat  for  certain  pur- 
poses, and  often  is  termed  seaplane. 

Future  of  the  Airplane. — In  order  to  be  commer- 
cially successful  and  have  a  commercial  future  after 
the  war,  the  following  weak  points  in  airplane  de- 
sign must  be  rectified. 

1.  Motor. — Airplane   motors   are  imperfect   and 
unreliable  at  present  and  there  must  be  considerable 
progress  before  this  type  of  motor  which  is  very 
light  and  delicate  can  be  considered  as  reliable  or 
can  be  made  in  large  enough  quantities  to  cut  down 
the  cost. 

2.  Landing. — The  necessity  of  landing  at  consid- 
erable speed,  say  40  to  50  miles  per  hour,  requires 
a  wide  flat  space,  such  as  is  not  easy  to  find,  and  if 
the  present  type  of  airplane  is  to  become  commer- 
cially numerous,   a  large  number  of  landing  fields 
must  be  developed  all  over  the  country. 

3.  Danger. — The  airplane  is  by  no  means  so  dan- 
gerous as  the  public  has  been  led  to  think  from  the 
exploits  of  the  daredevil  circus  performers  of  the 
past  10  years;  with  careful  manipulation  it  will  make 
trips  day  after  day  without  any  damage.     However, 
it  is  not  a  foolproof  machine  and  there  remains  an 
element  of  danger  on  this  account,  which  it  is  hoped 
will  one  day  be  eliminated. 

Future  Uses  of  the  Airplane. — Future  uses  of  the 
airplane  are  many  after  the  war  is  over.  The  postal 
service  of  several  governments  are  considering  this 
means  of  mail  delivery;  the  sports  use  as  in  the  past 


345544 


38  MANUAL  OF  AVIATION  PRACTICE 

will  continue  to  flourish;  express  carrying  may  be 
expected  in  inaccessible  countries  where  railroads 
and  roads  do  not  give  access  and  where  high-speed 
delivery  by  countless  airplanes  would  aid  materially 
in  the  development  of  newly  opened  countries.  For 
airplane  transportation  will  require  no  expensive 
right-of-way,  rubber-tire  renewals,  etc.  Minor  uses 
of  airplanes  are  on  such  duties  as  forest-fire  patrol, 
working  at  life-saving  stations,  etc. 

American  Airplane  Industries. — The  magnitude 
of  the  airplane  industry  in  this  country  is  great, 
although  not  so  great  as  in  Europe.  Leading  busi- 
ness men  have  invested  in  this  industry  with  the  firm 
belief  that  it  will  become  a  profitable  one,  irrespec- 
tive of  war.  We  see  a  number  of  leading  bankers 
and  also  automobile  manufacturers  in  various  parts 
of  the  country  putting  their  money  into  this  new 
industry.  Now  that  a  great  demand  has  sprung  up 
on  o.ur  side  of  the  water  for  airplanes,  we  will  expect 
to  see  this  industry  increase  more  rapidly  still.  The 
only  result  can  be,  from  all  the  interest  and  import- 
ance attached  to  aviation,  that  after  the  war  is  over, 
large  commercial  uses  will  develop  which  will  offer 
employment  to  those  who  go  into  the  work  at  this 
time  for  military  reasons.  No  one  can  predict 
exactly  what  turn  the  situation  will  take,  but  there 
is  every  indication  that  aviation  has  graduated  from 
the  primary  class  of  experimental  work  and  is  to  be 
considered  now  as  an  industry  along  with  the  auto- 
mobile business,  motor-boat  business,  etc. 


CHAPTER  III 
PRINCIPLES  OF  FLIGHT 

Support  of  an  Airplane  by  Its  Wings.— An  air- 
plane is  supported  just  as  definitely  as  though  on 
top  of  a  post,  and  by  the  same  law,  namely  reaction. 
If  you  try  to  sweep  the  air  downward  with  a  wing 
held  at  a  slight  angle,  the  air  just  before  it  consents 
to  be  pushed  downward,  delivers  a  momentary  re- 
action which  is  upward.  If  you  have  a  bag  of  air 
in  your  hand  it  exerts  no  push  upward  of  course; 
but  the  minute  you  give  it  a  quick  push  downward 
it  resists,  due  to  its  inertia,  thus  delivering  an 
upward  " reaction"  against  your  hand. 

Whenever  you  move  anything,  it  reacts  an 
amount  just  equal  to  the  force  that  is  moving  it; 
if  you  move  a  bullet  out  of  a  gun,  just  before  start- 
ing the  bullet  reacts  and  you  have  "kick."  If 
you  should  shoot  a  thousand  guns  downward,  the 
reaction  would  be  considerable,  and  for  the  instant 
might  be  sufficient  to  support  heavy  weight. 

The  airplane  is  a  device  for  pushing  downward 
millions  of  little  bullets,  made  out  of  air  and  ex- 
ceedingly small  and  light.  The  wing  of  an  air- 
plane sweeps  through  these  bullets,  or  molecules, 
of  air  like  a  horizontal  plow,  wedges  the  particles 
downward  in  vast  numbers  and  in  a  continual 

39 

4 


40  MANUAL  OF  AVIATION  PRACTICE 

stream,  making  up  in  amount  what  is  lacking  in 
weight,  so  that  as  long  as  the  airplane  rushes  along, 
there  are  many  thousands  of  cubic  feet  of  air  forced 
down  beneath  its  wings,  delivering  up  a  reaction 
that  results  in  complete  support  for  the  machine. 
This  reaction  is  just  as  definite  and  secure  as  though 
the  machine  were  supported  from  the  ground  on 
wheels,  but  it  disappears  entirely  when  the  airplane 
is  at  rest.  Part  of  the  whir  of  a  training  machine 
as  it  glides  back  to  earth  is  made  by  the  air  driven 
downward  from  the  wings;  the  same  phenomenon 
may  be  noticed  when  a  bat  flies  close  to  your  ears 
at  night,  and  if  you  were  a  few  feet  below  the  air- 
plane as  it  flew,  you  would  feel  the  rush  of  air 
driven  downward  from  its  wings  (see  Fig.  16). 

The  net  result  of  all  the  reactive  pushes  from  this 
air  is  lift.  It  may  amount  to  several  pounds  for 
every  square  foot  of  the  wing  surface. 

This  is  all  that  need  be  said  about  why  the  air 
supports  an  airplane;  all  you  have  to  remember 
is  that  as  long  as  you  have  the  forward  sweeping 
movement,  you  will  have  the  lift. 

The  forward  movement  is  absolutely  essential, 
however,  and  to  maintain  it  requires  a  lot  of  horse- 
power and  gasoline.  For  it  is  by  means  of  the 
engine  and  propeller  that  this  forward  movement 
is  maintained.  The  engine  is  a  device  for  creating 
forward  movement — the  propeller  drives  the  ma- 
chine ahead  in  exactly  the  same  way  as  is  the  case 
in  a  torpedo,  or  steamboat. 

Lift. — Assuming  that  we  have  all  the  forward 


PRINCIPLES  OF  FLIGHT 


41 


42  MANUAL  OF  AVIATION  PRACTICE 

motion  needed,  let  us  now  investigate  the  lift  that 
results.  Experimenters  such  as  the  Wrights  and 
others  have  found  out  how  to  get  this  lift  most  con- 
veniently. Lift  depends  upon  the  four  following 
factors : 

1.  Area. 

2.  Density  of  air. 

3.  Angle  of  incidence. 

4.  Speed  of  motion. 

1.  Relation  of  Area  of  Wings  to  Support. — Con- 
sider a  small  wing;  suppose  it  to  be  held  by  hand 
outside  a  train  window  in  a  given  attitude,  its  area 
being  1  sq.  ft.  It  tends  to  lift  a  certain  amount, 
say  5  Ib.  Now  increase  its  size  to  2  sq.  ft.  and  it 
will  lift  with  10-lb.  force,  tending  to  get  away  from 
your  grasp.  Rule:  When  only  the  area  of  a  wing 
is  changed,  its  lift  varies  with  the  area.  If,  as 
above  mentioned,  you  can  get  5  Ib.  of  lift  from  each 
square  foot  of  wing  surface,  you  can  by  the  same 
sign  get  10-lb.  of  lift  from  2  sq.  ft.  And  if  you 
have  500  sq.  ft.  of  surface  you  can  get  2500  Ib.  of 
lift. 

Regarding  area  of  wing  surface,  the  pilot  does 
not  have  to  worry  in  a  flight  since  he  can  do  noth- 
ing to  change  it  anyway.  All  he  needs  to  know 
is  that  in  different  airplanes  small  wing  area  ac- 
companies high  speed  and  small  weight-carrying 
capacity,  as  in  the  case  of  the  Fokker  and  Sopwith 
speed  scouts  (see  Fig.  17).  Conversely,  large 
wing  areas  are  used  for  heavy  load  carrying  and 


PRINCIPLES  OF  FLIGHT 


43 


FIG.  17. — Diagram  showing  that  in  fast  airplanes   wings  are  small; 

in  slow  airplanes  wings  are  large. 

(Above)     Small  wings;  speed  115  mi.  per  hr.;  for  fighting.     One  seat. 
(Below)    Large  wings;  speed  80  mi.  per  hr.;  for  reconnaissance.     Two  seats. 


44 


MANUAL  OF  AVIATION  PRACTICE 


slow  speed  (see  Fig.  18).  Speed  and  weight- 
carrying  capacity  thus  appear  to  be  antagonistic 
and  can  not  both  be  attained  with  efficiency,  but 
only  at  the  expense  of  enormous  power.  The.  in- 
compatibility between  high  speed  and  weight  carry- 
ing keeps  the  designer  busy  in  efforts  toward  a 
reconciliation. 


WING  AREA  26OO  SQ.FT. 
WEIGHT  20000  LB. 


WING  AREA  350  SQ.  FT. 
WEIGHT  2100  LB. 


FIG.   18.  —  Diagram  showing  use  of  large  wings  for  heavy  airplanes, 
and  small  wings  for  light  airplanes. 


2.  Density.  —  The  second  factor  affecting  the  lift 
is  the  character  of  the  air  itself.  I  refer  to  the 
density  of  the  air.  The  heavier  each  particle  of 
air  becomes,  the  more  reaction  it  can  furnish  to 
the  wing  that  drives  it  downward;  so  on  days  when 
the  barometer  is  high  the  wing  will  lift  more  than 
on  other  days.  Now  the  air  is  heaviest,  or  most 


PRINCIPLES  OF  FLIGHT  45 

dense,  right  near  the  ground ;  because  in  supporting 
the  50  miles  or  so  of  air  above  it,  it  becomes  com- 
pressed and  has  more  weight  per  cubic  foot.  There- 
fore, the  wing  gets  more  lift  at  a  low  altitude  than 
at  a  high.  Some  airplanes  will  fly  when  low  down 
but  won't  fly  at  all  high  up.  In  Mexico,  for  instance, 
when  the  punitive  expedition  started  out  they 
were  already  at  an  altitude  of  several  thousand  feet 
above  sea  level.  The  airplanes  had  been  built 
for  use  at  places  like  New  York  and  England,  close 
to  sea  level,  and  when  our  army  officers  tried  to 
fly  with  them  in  Mexico,  they  would  not  fly 
properly,  and  the  factory  had  to  redesign  them. 

Regarding  density,  the  pilot  should  know  that 
for  a  low  density  he  should  theoretically  get  a  high 
speed.  As  density  decreases,  high  up  in  the  air, 
the  speed  tends  to  increase,  and  moreover  he  gets 
more  speed  for  the  same  amount  of  gasoline.  Un- 
fortunately, at  an  altitude  the  motor  power  falls 
off,  so  that  nowadays  the  speed  is  not  faster  high 
up  than  low  down;  but  when  the  motor  builders 
succeed  in  designing  their  motors  to  give  the  same 
horsepower  at  20,000  ft.  as  they  do  on  the  ground, 
airplanes  will  be  able  to  reach  terrific  speed  by 
doing  their  work  above  the  clouds. 

It  is  found  desirable  to  give  large  wings  to  air- 
planes which  are  going  to  fly  at  high  altitudes,  so 
as  to  offset  the  lack  of  density  by  an  increase  in 
area,  thus  leaving  the  angle  range — that  is,  the 
speed  range — as  large  as  possible.  The  army  air- 
planes in  Mexico  mentioned  above  were  simply 


46  MANUAL  OF  AVIATION  PRACTICE 

given  a  new  set  of  larger  wings  to  offset  the  lower 
air  density  in  Mexico,  and  thereafter  flew  better. 

3.  Angle  of  Incidence. — The  angle  of  incidence  is 
denned  as  the  angle  between  the  wing-chord  and  the 
line  of  flight.  The  line  of  flight  is  the  direction  of 
motion  of  the  airplane,  and  is  distinct  from  the  axis 
of  the  airplane  which  corresponds  with  the  line  of 
flight  only  for  a  single  angle  of  incidence.  If  the 
line  of  flight  is  horizontal,  the  airplane  may  be 
flying  tail-high,  tail-level,  or  tail-low;  that  is,  its 
axis  may  have  varying  positions  for  a  given  line  of 
flight.  This  is  true,  if  the  line  of  flight  is  inclined, 
as  in  climbing.  It  is  a  mistake  to  confuse  the  line 
of  flight  with  the  axis  of  the  machine. 

The  angle  of  incidence  of  the  wings  of  the  U.  S. 
training  machine  may  have  any  value  from  15° 
down.  When  the  angle  is  smaller  the  lift  of  the 
wings  is  smaller.  Consider  the  model  wing  held 
out  of  a  train  window;  if  its  front  edge  is  tilted  up  to 
an  angle  of  15°  with  the  line  of  motion  it  will  lift 
say  1  lb.;  if  reduced  to  a  10°  angle,  it  will  lift  less, 
say  %  lb.  A  model  of  the  training-machine  wing 
could  be  tilted  down  to  an  angle  several  degrees  less 
than  zero  before  its  lift  disappeared,  because  it  is  a 
curved,  not  a  flat  wing;  this  angle  would  be  the 
"neutral-lift"  angle;  notice  then  that  0°  is  not  a 
neutral-lift  angle,  and  therefore  may  be  used  in 
flight. 

If  the  model  wing  were  tilted  up  to  an  angle 
greater  than  15°,  the  lift  would  not  increase  any 
more,  but  would  be  found  to  decrease.  For  this 


PRINCIPLES  OF  FLIGHT  47 

wing,  15°  is  called  the  critical,  or  " Stalling" 
angle,  beyond  which  it  is  unwise  to  go. 

4.  Velocity. — If  the  model  wing  which  is  imagined 
to  be  held  out  of  the  car  window,  is  held  now  in  a 
fixed  position  at  a  given  angle  of  incidence,  any 
change  of  the  train's  speed  will  result  in  a  change 
of  lift;  should  the  speed  rise  from  30  miles  per 
hour  to  double  this  value,  the  lift  would  increase 
enormously,  fourfold  in  fact. 

Lift  varies  as  the  square  of  the  speed.  Thus  any 
increase  or  decrease  of  speed  results  in  a  great  in- 
crease or  decrease  of  lift. 

Interdependence  of  Angle  of  Incidence  and 
Velocity. — The  four  factors  above  mentioned  all 
contribute  to  the  lift;  if  in  an  airplane  wing  each 
factor  be  given  a  definite  value,  the  resulting  lift  is 
determined  according  to  the  formula: 

L  =  KrAV2 
where      L  is  lift. 

K  is  a  coefficient  referring  to  the  angle. 
A  is  the  area. 
V  is  the  velocity. 
r  is  the  density. 

Two  only  of  these  quantities  change  materially  in 
flight,  the  angle  and  the  velocity;  the  lift  itself  re- 
mains substantially  the  same  under  most  normal 
circumstances.  The  angle  always  changes  simul- 
taneously with  the  velocity,  increasing  when  the 
velocity  decreases.  Thus  the  drop  of  lift  due  to 


48  MANUAL  OF  AVIATION  PRACTICE 

velocity  decrease  is  balanced  by  gain  of  lift  due  to 
angle  increase,  and  the  lift  remains  unchanged  when 
speed  changes. 

Speed  change  then  requires  that  the  pilot  alter 
the  angle  of  incidence  simultaneously  with  the 
throttle;  so  there  are  two  things  to  do,  unlike  the 
case  of  the  automobile  where  only  the  throttle  is 
altered. 

Minimum  Speed.— When,  in  slowing  up  an  air- 
plane, the  angle  of  incidence  reaches  the  15°  limit, 
no  further  decrease  of  speed  is  allowable;  therefore, 
the  critical  angle  determines  the  minimum  limit 
of  speed.  If  for  any  reason  the  machine  exceeds 
the  15°  limit,  it  must  speed  up  to  gain  support;  that 
is,  the  pilot  has  to  increase  angle  and  speed  simul- 
taneously instead  of  oppositely. 

Efficiency  of  Airplane  Wings. — I  said  at  the  be- 
ginning of  this  chapter  that  the  airplane  was  a 
device  for  pushing  down  an  enormous  quantity  of 
air.  A  certain  amount  of  force  has  to  be  furnished 
in  order  to  keep  the  airplane  moving,  and  this  force 
is  furnished  by  the  engine  and  propeller.  The 
propeller  by  giving  a  certain  amount  of  push  in  a 
horizontal  direction  to  the  airplane  wing  enables 
this  wing  to  extract  from  the  air  ten  or  twenty 
times  this  amount  of  push  in  a  vertical  direction; 
that  is,  the  airplane  wing  will  give  you  10  Ib.  or 
more  of  lifting  in  exchange  for  1  Ib.  of  push. 

The  propeller  push  is  necessary  to  overcome  the 
drift  or  resistance  of  the  wings  to  forward  motion. 
It  appears  then  that  the  airplane  wing  as  it  moves 


PRINCIPLES  OF  FLIGHT 


49 


through  the  air  has  two  forces  on  it,  one  acting 
straight  up  and  called  "lift,"  the  other  acting 
straight  back  and  called  "drift"  (see  Fig.  19).  The 
lift  is  several  times  greater  than  the  drift,  and  the 
situation  is  quite  analogous  to  that  of  a  kite, 


>  .LIFT 


FIG.  19. 

Lift  and  Drift.  —  Lift  is  perpendicular  to  line  of  flight,  drift  is  parallel. 

Angle  of  Incidence.  —  Wing  in  position  shown  has  angle  of  5°  if  moving  in 
direction  "A,"  10°  if  in  direction  "B;"  and  a  negative  angle  of  4°  if  moving  in 
direction  "C."  In  the  last  case  it  is  moving  along  its  neutral-lift-line,  lift 
becomes  zero. 


which  rises  upward  in  the  air  due  to  its  lift  but  at 
the  same  time  drifts  backward  with  the  wind  due 
to  its  drift.  In  the  case  of  the  kite  the  string  takes 
up  an  angle  which  just  balances  the  joint  effect  of 
the  lift  and  drift, 


50  MANUAL  OF  AVIATION  PRACTICE 

The  efficiency  of  an  airplane  wing  is  indicated  by 
the  ratio  of  lift  to  drift,  and  for  a  given  lift,  the 
efficiency  is  best,  therefore,  for  small  drift.  If  the 
lift  is  1900  Ib.  and  the  wing  drift  190  lb., 

Lift  or  weight       1900 
'Wing  drift       :I90  = 

Factors  Determining  Best  Efficiency. — It  goes 
without  saying  that  an  airplane  wing  should  attain 
the  best  efficiency  it  can,  and  there  are  several  ways 
of  doing  this. 

The  first  relates  to  the  question  of  angle  of  inci- 
dence; we  have  already  discussed  the  effect  of  angle 
on  lift,  but  when  we  come  to  discuss  its  effect  on 
efficiency  we  find  that  there  is  only  one  angle  at 
which  we  can  get  the  best  efficiency.  This  is  a 
small  angle,  about  3°  to  6°;  at  this  angle  the  lift  is 
nowhere  near  as  much  as  it  would  be  at  10°  or  15°, 
but  the  drift  is  so  small  compared  to  the  lift  that  it  is 
found  desirable  in  airplanes  to  employ  these  small 
angles  for  normal  flight.  As  the  angle  increases 
above  this  value  of  maximum  efficiency,  the  effi- 
ciency drops  off,  and  when  you  get  up  to  the  stalling 
angle,  the  efficiency  becomes  very  low  indeed  (see 
Fig.  20). 

The  second  way  to  get  good  efficiency  is  to  choose 
the  shape  of  the  wings  properly.  For  instance, 
early  experimenters  tried  to  get  results  with  flat 
wings,  and  failed  completely,  for  the  flat  wing 
proved  to  be  very  inefficient.  When  it  was  observed 
that  birds  had  curved  wings,  this  principle  was  ap- 


PRINCIPLES  OF  FLIGHT 


51 


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0        10       ?0      30      40       50       60      70    *  60 

C.P  FROM  LEADING  EDGE-PERCENT  CHORD 

FIG.  20. — Wing  characteristics. 

Curves  showing  lift,  drift,  efficiency,  and  center  of  pressure  travel  of  typical 
training-airplane  wing,  as  determined  in  Aerodynamical  Laboratory. 


52 


MANUAL  OF  AVIATION  PRACTICE 


plied  to  early  experiments  and  then  for  the  first 
time  man  was  able  to  obtain  support  in  a  flying 
machine.  The  fundamental  principle  of  efficiency 
in  wings  is  that  they  must  be  curved,  or  cambered,  as 
it  is  sometimes  called.  This  is  because  as  the  wing 
rushes  onward  it  wants  to  sweep  the  air  downward 
smoothly  and  without  shock,  as  can  be  done  only 
when  the  wing  is  curved  (see  air  flow,  Fig.  21). 


FIG.  21. — Efficiency  of  curved  and  flat  wing. 

(a)   Air  flow  past  curved  wing  is  smooth  without  much  eddying ;  (6)  air  flow 
past  flat  wing  produces  eddies  above  it. 

The  question  of  wing  curvature  is  exceedingly 
important  then;  we  find  that  the  curvature  of  its 
upper  surface  is  particularly  so.  We  notice  that 
airplane  wings  all  have  a  certain  thickness  in  order 
to  enclose  the  spars  and  ribs;  it  is  not  necessarily  a 
disadvantage  for  them  to  be  thick,  due  to  the  fact 
that  the  upper  curve  of  the  wing  does  most  of  the 
lifting  anyway,  and  the  lower  side  is  relatively 
unimportant.  You  can  make  the  lower  surface 
almost  flat,  without  much  hurting  the  effect  of  the 
wing,  so  long  as  the  upper  surface  remains  properly 


PRINCIPLES  OF  FLIGHT 


53 


curved.  However,  the  upper  surface  must  be  ac- 
curately shaped,  and  is  so  important  that  in  some 
machines  we  find  cloth  is  not  relied  on  to  maintain 
this  delicate  shape,  but  thin  wood  veneer  is  used  (I 
refer  to  the  front  upper  part  of  the  wing).  In 
general,  then,  wings  are  thick  toward  the  front  and 
taper  down  to  a  thin  trailing  edge. 

You  may  wonder  how  it  was  found  that  the  upper 
surface  of  the  wing  was  the  most  important;  and  I 


MONOPLANE 


BIPLANE 

FIG.  22. — Diagram  of  vacuum  and  pressure  on  airplane  wings. 
Note  in  biplane  reduced  vacuum  on  bottom  wing. 

will  say  that  this  was  one  of  the  interesting  dis- 
coveries of  the  early  history  of  aerodynamics. 
People  at  first  thought  that  a  wing  sweeping  through 
the  air  derived  its  support  entirely  from  the  air 
which  struck  the  bottom  of  the  wing,  and  they 
assumed  that  if  the  bottom  of  the  wing  were  properly 
shaped,  the  top  did  not  matter;  that  is,  all  the 
pressure  in  the  air  was  delivered  up  against  the 


54  MANUAL  OF  AVIATION  PRACTICE 

bottom  surface.  But  a  French  experimenter  con- 
ceived the  idea  of  inserting  little  pressure  gages  at 
various  points  around  the  wing.  He  found,  it  is 
true,  that  there  was  considerable  pressure  exerted 
in  the  air  against  the  bottom  of  the  wing;  but  he 
found  a  more  surprising  fact  when  he  measured  the 
condition  above  the  wing.  When  he  applied  his 
gage  to  the  upper  surface  of  the  wing,  it  read  back- 
ward, that  is,  showed  a  vacuum,  and  a  very  pro- 
nounced one.  He  found  that  there  was  a  vacuum 
sucking  the  top  part  of  the  wing  upward  twice  as 
hard  as  the  pressure  underneath  was  pushing,  so 
that  two-thirds  of  the  total  lift  on  this  wing  was  due 
to  vacuum  above  it  (see  Fig.  22). 

In  the  diagram  the  shaded  area  on  top  of  the  wing 
represents  vacuum  above,  that  below  the  wing 
represents  pressure  beneath. 


-FT 


ASPECT  RATIO  ASPECT  RATIO 

5  7 

FIG.  23. — Wings  of  small  and  large  aspect  ratio. 

Aspect  Ratio. — The  third  factor  in  wing  efficiency 
has  to  do  with  the  plan  shape.  It  was  early  found 
that  square  wings  were  not  much  good,  and  that  if 
you  made  them  wide  in  span  like  those  of  a  bird,  the 
efficiency  was  best  (see  Fig.  23).  Aspect  ratio  is 
the  term  which  gives  the  relation  of  the  span  to 


PRINCIPLES  OF  FLIGHT 


55 


the  fore  and  aft  dimension  of  the  wing,  and  this 
relation  is  usually  equal  to  six  or  so.  The  reason 
why  large  aspect  ratios  are  advantageous  is  as 
follows : 

The  tips  of  all  wings  are  inefficient,  because  they 
allow  the  air  to  slip  sideways  around  the  ends,  and 
there  is  all  the  trouble  of  disturbing  this  air  without 
extracting  any  considerable  lift  from  it.  In  a  wide- 
span  wing  these  inefficient  wing  tips  are  only  a  small 

LEADING       EDGE: 


!    \    S 


TRAILING       EDGE 


FIG.  24. — Diagram  illustrating  aspect-ratio  effect. 

Arrows  show  direction  of  air  flow  past  plate;  note  that  air  escapes  sideways 
around  sides  of  plate.  This  phenomenon  occurs  at  the  tips  of  all  airplane  wings 
and  accounts  for  small  efficiency  of  narrow-span  wings. 

percentage  of  the  total  area,  but  in  a  small-span 
wing  they  may  be  an  important  consideration  (see 
Fig.  24). 

Wing  Arrangements. — All  the  foregoing  remarks 
in  this  chapter  have  applied  only  to  a  single  wing. 
They  apply  in  general  to  double  or  triple  wings  (bi- 
planes and  triplanes),  but  the  matter  of  arranging 
multiple  wings  affects  the  efficiency. 

The  monoplane  with  its  single  layer  of  wings  is 
the  most  efficient  type  of  flying  machine.  We  find 
if  we  arrange  wings  into  the  biplane  shape  that  the 


56  MANUAL  OF  AVIATION  PRACTICE 

presence  of  the  upper  wing  interferes  with  the  vacuum 
formed  above  the  lower  wing,  and  the  effi- 
ciency decreases  (see  Fig.  22).  The  same  is  true  of 
the  triplane  and  the  quadruplane  arrangement.  If 
all  we  wanted  in  airplanes  was  efficiency,  we  would 
use  monoplanes,  but  the  biplane  is  pretty  popular 
now  in  spite  of  its  low  efficiency;  this  is  because  it 
can  be  much  more  strongly  trussed  than  the  mono- 
plane, and  also  because  of  the  fact  that  sufficient 
area  may  be  secured  with  less  span  of  wings. 

It  may  be  said  that  the  low  efficiency  of  the  bi- 
plane can  be  somewhat  relieved  by  spacing  the  upper 
and  lower  wings  at  a  considerable  distance  apart; 
but  if  they  are  spaced  at  a  distance  much  greater 
than  the  chord,  it  requires  extra  long  struts  and 
wires,  and  the  resistance  and  weight  of  these  will 
offset  the  advantage  of  wider  spacing;  so  that  prac- 
tically biplane-wing  efficiency  may  be  taken  as  85 
per  cent,  of  monoplane  efficiency. 

It  remains  to  mention  the  tandem  arrangement, 
used  in  all  airplanes,  where  the  tail  is  a  tandem  sur- 
face in  conjunction  with  the  wings.  A  surface 
located  in  the  position  of  an  airplane  tail  is  at  a  dis- 
advantage and  shows  low  efficiency  for  flight  pur- 
poses. This  is  because  the  main  wings  deflect  the 
air  downward  and  when  the  tail  comes  along  it  meets 
air  which  has  a  more  or  less  downward  trend,  in- 
stead of  encountering  fresh,  undisturbed  air  (see 
Fig.  16). 

Resistance  of  an  Airplane  to  Motion.— Earlier  in 
this  chapter  the  support  of  an  airplane  was  explained 


PRINCIPLES  OF  FLIGHT  57 

and  it  was  seen  that  the  weight  was  exactly  equalled 
by  the  lift  or  support;  it  was  also  explained  that  the 
production  of  this  lift  required  considerable  force 
in  moving  the  wings  rapidly  through  the  air.  It  is 
not  only  the  wings,  however,  which  require  force  to 
overcome  the  resistance  to  motion.  In  order  to 
have  any  wings  at  all  it  is  unfortunately  necessary 
to  supply  also  struts,  wires,  etc.,  for  bracing  these 
wings,  also  a  motor  and  seat  for  the  passenger, 
which  are  usually  included  inside  a  fuselage,  also 
wheels  for  landing  and  various  control  surfaces. 
None  of  these  accessories  to  the  wings  contribute 
material  lift,  but  they  involve  a  large  amount  of 
resistance  which  is  therefore  a  dead  loss.  Note 
carefully  that  there  are  two  distinct  sorts  of  resist- 
ance: (1)  that  of  the  wings,  which  is  the  necessary 
price  paid  for  securing  lift ;  (2)  that  of  all  the  rest  of 
the  machine,  in  return  for  which  nothing  beneficial 
is  received,  and  which  therefore  has  sometimes  been 
called  " parasite"  or  " deadhead"  resistance. 

In  a  typical  training  machine  the  total  resistance 
to  be  overcome  if  forward  motion  is  maintained  is  as 
follows:  (See  Fig.  26.) 

At  72  miles  per  hour: 

Wings 160  Ib. 

f  Fuselage 75 

„       ,     Wiring .70 

Deadhead    •„, 

<  Struts 20  >         195 

resistance     ,*•      n 

I  Miscellaneous 

I  Balance 30  J 

Total..  .   355  Ib. 


58  MANUAL  OF  AVIATION  PRACTICE 

At  a  speed  of  57  miles  per  hour: 

Wings 158  Ib. 

Deadhead  resistance 130 

Total ' 288  Ib. 

At  a  speed  of  43  miles  per  hour: 

Wings 350  Ib. 

Deadhead  resistance 125 

Total 475  Ib. 

It  is  seen  that  the  above  resistance  values  total 
to  the  highest  figure  at  the  lowest  speed,  and  that 
the  lowest  value  of  resistance  occurs  at  an  interme- 
diate speed;  the  resistance  decreases  as  the  speed 
decreases  from  73  to  57  miles  per  hour;  but  a  further 
decrease  in  speed  finds  the  resistance  running  up 
rapidly  so  that  at  minimum  speed  the  resistance  is 
very  great  again.  This  is  due  to  the  fact  that  at 
high  speeds  the  deadhead  resistance  exceeds  that  of 
the  wings  but  at  slow  speeds  although  the  deadhead 
resistance  is  very  small,  the  wings  being  turned  up 
to  a  large  angle  within  the  air,  have  a  resistance 
which  is  at  its  maximum.  This  seems  clear  enough 
when  we  remember  that  the  lift  of  the  wings  remains 
the  same  as  the  angle  decreases  (and  speed  goes  up) 
but  that  the  efficiency  of  the  wings  increases  so  that 
the  wing  resistance  is  a  smaller  fraction  of  the  lift 
at  high  speed  than  at  low  speed. 

Cause  of  Resistance. — Wing  resistance,  which 
is  affected,  as  mentioned  previously,  by  the  wing 
curvature,  can  not  be  decreased  unless  new  and 


PRINCIPLES  OF  FLIGHT 


59 


improved  sorts  of  wings  are  invented.  As  to  dead- 
head resistance,  it  may  be  decreased  in  future  by 
methods  of  construction  which  eliminate  unessen- 
tial parts.  In  a  high-speed  airplane  in  this  country 
an  attempt  was  made  to  eliminate  the  wires  alto- 
gether and  most  of  the  struts  (because  the  wiring 
is  one  of  the  largest  single  items  of  deadhead  resist- 
ance); so  far  the  attempt  has  failed  for  structural 
reasons.  In  the  monoplane  type  of  airplane  of 
course  the  struts  are  eliminated,  which  is  an  advan- 
tage from  the  standpoint  of  resistance. 


FIG.  25. — Diagram  illustrating  advantage  of  streamline  shape. 

Note  large  eddy  disturbance  and  vacuum  behind  round  shape,  causing  high 
resistance. 

As  long  as  struts,  wires,  etc.,  are  used  at  all,  the 
minimum  resistance  can  be  secured  by  giving  them 
a  proper  "  stream-line "  shape.  The  stream-line 
shape  is  one  in  which  the  thickest  part  is  in  front 
and  tapers  off  to  a  point  in  the  rear,  like  a  fish.  If, 
for  instance,  we  take  round  rods  instead  of  the 


60  MANUAL  OF  AVIATION  PRACTICE 

struts  of  the  training  machine  above  mentioned  and 
having  the  same  thickness,  the  resistance  might  be 
80  Ib.  instead  of  20  Ib. ;  and  if  we  take  a  rod  whose 
shape  is  elliptical  with  its  axes  in  a  ratio  of  1  to  5 
the  resistance  might  be  40  Ib.  instead  of  20  Ib. ;  and 
if  we  took  the  stream-line  struts  out  of  the  training 
machine  and  put  them  back  sharp  edge  foremost,  the 
resistance  would  be  increased.  The  advantage  of 
the  stream-line  shape  is  that  it  provides  smooth  lines 
of  flow  for  the  air  which  has  been  thrust  aside  at  the 
front  to  flow  back  again  without  eddies  to  the  rear. 
This  is  not  possible  in  the  case  of  the  round  strut, 
behind  which  will  be  found  a  whirl  of  eddies  result- 
ing in  a  vacuum  that  tends  to  suck  it  backward.  By 
fastening  a  stream-line  tail  behind  the  round  rod  the 
eddies  are  greatly  reduced,  as  is  the  vacuum.  The 
wires  of  the  airplane  are  subject  to  the  same  law  and 
if  the  training  machine  above  mentioned  had 
stream-line  wires  instead  of  round  wires  we  might 
expect  them  to  have  less  than  70  Ib.  resistance.  The 
fuselage  should  always  be  given  as  nearly  a  stream- 
line shape  as  the  presence  of  the  motor  and  tanks 
will  permit;  and  it  must  all  be  inclosed  smoothly  in 
"doped"  fabric  in  order  that  the  air-flow  phenomena 
may  operate.  As  for  the  wheels,  they  must  of  ne- 
cessity be  round,  but  by  enclosing  them  with  fabric 
the  air  flow  past  them  is  more  easy  and  the  resistance 
may  be  halved. 

Total  Resistance.— The  necessity  has  been  ex- 
plained of  discriminating  between  wing  and  dead- 
head resistance;  if  we  are  talking  about  wings  we 


PRINCIPLES  OF  FLIGHT  61 

may  ignore  everything  except  the  wing  resistance 
(commonly  called  "wing  drift"),  but  if  we  are  talk- 
ing about  the  whole  airplane,  we  then  must  refer  to 
the  total  resistance,  which  includes  all  the  others 
and  is  overcome  by  the  propeller  thrust.  "Skin- 
friction"  resistance  has  not  been  mentioned  nor 
need  it  be  more  than  to  say  that  any  surface  moving 
through  air  attributes  part  of  its  resistance  to  the 
actual  friction  of  the  air  against  it,  and  therefore 
should  be  as  smooth  as  possible. 

Motor  Power  Required  for  Flying. — The  reason 
resistance  interests  us  is  that  motor  power  is  re- 
quired to  propel  the  airplane  against  it;  more  and 
more  power  as  the  resistance  and  speed  increase. 
Obviously,  the  power  required  is  least  when  the  re- 
sistance is  small,  i.e.,  when  the  speed  is  interme- 
diate between  minimum  and  maximum.  It  takes 
more  power  to  fly  at  minimum  speed  than  at  this 
intermediate  speed.  Of  course  it  also  takes  more 
power  to  fly  at  maximum  speed,  where  again  the 
resistance  is  high. 

Maximum  Speed. — Ordinarily,  for  moderate 
speeds,  airplanes  have  a  margin  of  power  at  which 
the  throttle  need  not  be  opened  wide;  should  speed 
be  increased  the  resistance  and  horsepower  required 
will  increase  steadily  until  the  throttle  is  wide  open 
and  motor  "full  out;"  this  establishes  the  maxi- 
mum speed  of  an  airplane;  there  is  no  margin  of 
power,  no  climb  is  possible.  The  only  way  to  in- 
crease speed  is  to  use  the  force  of  gravity  in  addition 
to  the  motor  force.  It  may  be  interesting  to  know 


62  MANUAL  OF  AVIATION  PRACTICE 

what  is  the  maximum  possible  speed  in  the  case  of  a 
vertical  dive  with  the  motor  shut  off;  it  will  be  about 
double  the  maximum  horizontal  speed  as  may  be 
readily  seen  from  the  fact  that  the  thrust  in  the  di- 
rection of  motion  is  now  no  longer  horizontal  and 
equal  to  the  resistance  but  is  vertical  and  equal  to 
the  weight  of  the  machine;  that  is,  the  thrust  may  be 
increased  fivefold,  and  the  speed  resulting  will  be 
increased  correspondingly.  If  the  motor  be  running 
in  such  a  vertical  dive  the  velocity  may  be  slightly 
increased  though  at  this  speed  of  motion  the  pro- 
peller would  not  have  much  efficiency. 

There  is  danger  in  such  high  speeds ;  the  stresses 
in  the  machine  are  increased  several  times  merely  by 
the  increased  resistance,  and  if  the  angle  of  incidence 
should  be  suddenly  brought  up  to  a  large  value  at 
this  high  speed  the  stress  would  again  be  increased 
so  that  the  total  stress  increase  theoretically  might 
be  as  high  as  fourteen  times  the  normal  value,  thus 
exceeding  the  factor  of  safety.  It  is  for  such  rea- 
sons that  the  maximum  strength  is  desirable  in 
airplanes;  holes  must  not  be  carelessly  drilled  in  the 
beams  but  should  be  located  if  anywhere  midway 
between  the  top  and  bottom  edges,  where  the  stress 
will  be  least;  initial  stresses,  due  to  tightness  of  the 
wires,  should  not  be  too  great. 

Climbing  Ability.— Climbing  ability  refers  to  the 
number  of  feet  of  rise  per  minute  or  per  10  min. 
In  order  to  climb,  extra  horsepower  is  required 
beyond  that  necessary  for  more  horizontal  flight. 
The  machine  can,  for  instance,  fly  at  56  miles  per 


PRINCIPLES  OF  FLIGHT  63 

hour  at  which  speed  it  requires  43  hp.  If  now 
the  throttle  is  opened  up  so  as  to  increase  the  horse- 
power by  22,  making  a  total  of  65  hp.,  the  machine 
will  climb  at  the  rate  of  380  ft.  per  minute,  main- 
taining approximately  the  same  flight  speed.  If 
instead  of  65  hp.,  it  were  54  hp.  the  speed  of  climb 
would  be  about  one-half  of  the  380,  or  190  ft.  per 
minute;  the  flight  speed  again  remaining  approxi- 
mately as  before;  that  is,  any  margin  of  horsepower 
beyond  the  particular  value  of  horsepower  required 
may  be  used  for  climbing  without  material  change  of 
the  flight  speed.  It  is  necessary  here  to  state  that 
lift  does  not  increase  during  climb ;  and  while  for  the 
instant  that  a  climb  commences  there  may  be,  due 
to  acceleration,  more  lift  on  the  wings  than  balances 
the  weight,  this  does  not  remain  true  after  a 
steady  rate  of  climb  is  reached.  To  illustrate,  in 
a  wagon  drawn  uphill  by  horses  the  wheels  which 
support  the  wagon  do  not  exert  any  more  support 
than  on  the  level,  and  the  entire  force  to  make  the 
wagon  ascend  is  supplied  through  extra  hard  pulling 
by  the  horses.  Thus  in  a  climbing  airplane  the 
propeller  furnishes  all  the  climbing  force  and  lift 
is  no  greater  than  in  horizontal  flight.  In  fact,  the 
actual  lift  force  may  be  even  less,  as  the  weight  of 
the  airplane  is  partly  supported  by  the  propeller 
thrust  which  is  now  inclined  upward  slightly. 

To  secure  maximum  climbing  ability,  we  must 
determine  at  what  velocity  the  margin  of  motor 
power  is  the  greatest.  In  the  above-mentioned 
machine  we  know  that  the  horsepower  required  for 


64 


MANUAL  OF  AVIATION  PRACTICE 


support  is  least  for  a  speed  of  near  55  miles  per  hour, 
and  it  is  near  speed  where  therefore  the  excess   . 
margin  of  power  is  greatest  and  at  which  climbing 
is   best   done.     An   airplane   designed   chiefly   for 


50  60  70  60 

VELOCITY,  MILES  PER  HOUR 


FIG.  26. — Performance  curves  for  typical  tra: 


nmg  airplane. 


climbing  must  have  low  values  of  motor  power 
necessary  for  support,  namely,  must  have  small 
resistance,  therefore  small  size,  therefore  small 
weight. 


PRINCIPLES  OF  FLIGHT  65 

Gliding  Angle. — Gliding  angle  denotes  the  angle 
at  which  the  airplane  will  glide  downward  with 
the  motor  shut  off  and  is  spoken  of  as  1  in  5,  1 
in  6,  etc.,  according  as  it  brings  the  airplane  1  mile 
down  for  each  5,  6,  etc.,  miles  of  travel  in  the  line 
of  flight.  The  gliding  angle  of  a  machine  may  be 
found  by  dividing  the  total  resistance  into  the 
weight : 

Weight 
Gliding  angle  = 


Total  resistance 

In  the  above-mentioned  airplane  it  is  one  in  6.6 
when  the  resistance  is  288  lb.,  that  is,  when  the 
speed  is  57  miles  per  hour.  At  any  other  speed  the 
resistance  increases  and  hence  the  gliding  angle 
decreases.  Hence  the  importance  of  putting  the 
airplane  into  its  proper  speed  in  order  to  secure  the 
best  gliding  angle. 

The  Propeller. — The  propeller  or  "screw,"  by 
screwing  its  way  forward  through  the  air,  is  able 
to  propel  the  airplane  at  the  desired  velocity. 
Regarding  principles  of  propeller  action  the  matter 
can  be  hastily  summarized  in  the  following  brief 
lines.  The  propeller  blades  may  be  regarded  as 
little  wings  moving  in  a  circular  path  about  the 
shaft ;  and  they  have  a  lift  and  drift  as  do  the  regular 
wings.  The  lift  is  analogous  to  the  thrust;  to  secure 
this  thrust  with  least  torque  (drift)  the  blades  are 
set  at  their  most  efficient  angle  of  incidence,  and 
while  the  blade  appears  to  have  a  steep  angle  near 


66  MANUAL  OF  AVIATION  PRACTICE 

the  hub,  it  actually  meets  the  air  in  flight  at  the 
same  angle  of  incidence  from  hub  to  tip. 

Propeller  Pitch. — Pitch  is  best  defined  by  analogy 
to  an  ordinary  wood-screw ;  if  the  screw  is  turned  one 
revolution  it  advances  into  the  wood  by  an  amount 
equal  to  its  pitch.  If  the  air  were  solid,  a  propeller 
would  do  the  same,  and  the  distance  might  be  8  ft., 
say.  Actually  the  air  yields,  and  slips  backward, 
and  the  propeller  advances  only  6  ft.  Its  "slip"  is 
then  8  minus  6,  equals  2  ft.,  or  25  per  cent.  Such  a 
propeller  has  an  8-ft.  pitch,  and  a  25  per  cent.  slip. 

This  "slip  stream"  blows  backward  in  a  flight 
so  that  the  tail  of  an  airplane  has  air  slipping  past 
it  faster  than  do  the  wings.  Hence  the  air  forces 
at  the  tail  are  greater  than  might  be  expected. 
The  rudder  and  elevators  therefore  give  a  quicker 
action  when  the  propeller  is  rotating  than  when,  as 
in  the  case  of  a  glide,  it  is  not. 


.          ,  WASHOUT 

PROPELLER-*  Prevents  Anfi-dockmx 

Rotates  Clockwise  Rotation  ofAirp/z 

FIG.  27. — Washout  in  left-wing  tips. 


vane 


Washout. — Due  to  torque  of  the  motor,  the  air- 
plane tends  to  rotate  in  the  opposite  direction  to  the 
propeller.  This  tendency  may  be  neutralized  by 
giving  one  wing  tip  a  smaller  angle  of  incidence, 
called  "washout,"  so  that  the  machine  normally 
tends  to  neutralize  the  torque-effect. 


PRINCIPLES  OF  FLIGHT 


67 


PRINCIPLES  OF  AIRPLANE  EQUILIBRIUM 

Introductory. — Under  this  head  will  be  discussed : 
(a)  features  of  airplane  design  which  tend  to  main- 
tain equilibrium  irrespective  of  the  pilot;  (6) 
matters  of  voluntary  controlling  operations  by  the 
pilot.  As  regards  (a)  the  tendency  of  the  airplane 


FIG.  28. — Balances  of  forces  in  an  airplane. 

Weight  forward  of  lift,  thrust  below  resistance.     Thrust  equals  resistance, 
weight  equals  lift. 

toward  inherent  stability  acts  to  oppose  any  devia- 
tion from  its  course  whether  the  pilot  so  desires 
or  not.  The  more  stable  is  a  machine,  the  less 
delicately  is  it  controlled,  and  the  present  con- 
sensus of  opinion  among  pilots  is  that  a  50-50 


68  MANUAL  OF  AVIATION  PRACTICE 

compromise  between  stability  and  controlability  is 
the  best  thing. 

In  questions  of  airplane  equilibrium  the  starting 
point  is  the  center  of  gravity;  obviously,  if  the 
center  of  gravity  were  back  at  the  tail  or  up  at  the 
nose  there  would  be  no  balance;  the  proper  place 
for  it  is  the  same  spot  where  all  the  other  forces 
such  as  thrust,  lift  and  resistance  act;  there  it  is 
easy  to  balance  them  all  up.  But  it  is  not  always 
easy  to  bring  the  line  of  thrust  and  the  line  of  total 
resistance  into  coincidence,  because  the  line  of 
thrust  is  the  line  of  the  propeller  shaft  and  when 
this  is  high  up  as  in  the  case  of  some  pushers  it  may 
be  several  inches  above  the  line  of  resistance. 
And  as  the  thrust  is  above  the  resistance  there  is  a 
tendency  to  nose  the  machine  down;  to  balance 
which  the  designer  deliberately  locates  the  center 
of  gravity  sufficiently  far  behind  the  center  of  lift 
so  that  there  is  an  equal  tendency  to  tip  the  nose 
upward;  and  all  four  forces  mentioned  completely 
balance  each  other.  But  things  may  happen  to 
change  the  amount  or  position  of  these  forces 
during  flight,  and  if  this  does  happen  the  first  thing 
to  do  is  to  restore  the  balance  by  bringing  in  a  small 
new  force  somewhere.  In  an  actual  airplane  this 
small  restoring  force  is  supplied  at  each  critical 
moment  first,  by  the  tail,  etc.,  of  the  airplane  and 
second,  by  voluntary  actions  of  the  pilot.  The 
center  of  gravity  of  any  airplane  may  be  determined 
easily  by  putting  a  roller  under  it  and  seeing  where 
it  will  balance,  or  by  getting  the  amount  of  weight 


PRINCIPLES  OF  FLIGHT  69 

supported  at  the  wheels  and  tail,  according  to  the 
method  of  moments. 

Longitudinal  Stability. — Longitudinal  stability 
has  to  do  with  the  tendency  of  an  airplane  to 
maintain  its  proper  pitching  angle.  It  was  said 
above  that  the  four  forces  of  lift,  resistance,  thrust 
and  weight  always  exactly  balanced  due  to  their 
size  and  their  position.  Now  the  first  consideration 
about  longitudinal  stability  is  that  while  the 
centers  of  gravity  and  other  forces  remain  in  a  fixed 
position,  the  center  of  lift  changes  its  position  when- 
ever the  angle  of  incidence  (that  is  the  speed)  is 
changed.  The  phenomenon  of  shift  of  center  of 
pressure  applies  only  to  the  wings  and  to  the  lift 
(the  position  of  center  of  resistance  remains  prac- 
tically fixed  at  all  angles). 

Note  the  effect  on  center  of  pressure  position  of  a 
change  of  wing  angle  (see  Fig.  20).  The  wing  used 
on  the  U.  S.  training  machine  has  a  center  of  lift 
which  is  about  in  the  middle  of  the  wing  when 
flying  at  a  small  angle  of  maximum  speed;  but  if 
the  angle  is  increased  to  the  stalling  angle  of  15°, 
the  center  of  pressure  moves  from  midway  of  the 
wing  to  a  point  which  is  about  one-third  the  chord 
distance  of  the  wing  from  the  front  edge.  The  lift 
may  travel  about  %  foot,  and  it  is  equal  in  amount 
to  the  weight  of  the  machine  (that  is,  nearly  a  ton), 
and  the  mere  effect  of  changing  the  angle  from 
its  minimum  to  its  maximum  value  therefore  tends 
to  disturb  the  longitudinal  equilibrium  with  a 
force  which  may  be  represented  as  1  ton  acting  on  a 


70  MANUAL  OF  AVIATION  PRACTICE 

lever  arm  of  ^  ft.  Suppose  that  the  airplane  is 
balancing  at  an  angle  of  2°  so  that  the  center  of 
gravity  coincides  with  the  center  of  lift  for  this 
angle;  now  if  a  gust  of  wind  causes  the  angle  to 
increase  for  an  instant  to  2%°,  the  center  of  lift 
will  move  forward  and  tend  to  push  the  front  edge 
of  the  wing  up,  thus  increasing  the  angle  further  to 
2J^°.  Then  the  center  of  lift,  of  course,  moves 
further  forward  to  accommodate  the  increase  of 
angle,  and  in  a  fraction  of  a  second  the  wing 
would  rear  up  unless  it  were  firmly  attached  to  the 
airplane  body  and  held  in  its  proper  position  by  the 
tail.  Similarly  if  for  any  reason  the  proper  angle 
of  2°  were  decreased,  the  same  upset  would  follow, 
only  this  time  tending  to  dive  the  wing  violently 
to  earth.  This  tendency  is  neutralized  in  an  airplane 
by  the  "Penaud  Tail  Principle." 

There  are  certain  shapes  of  wings  in  which  the 
center  of  pressure  travels  in  the  reverse  direction; 
a  flat  plate,  for  example;  or  a  wing  having  its  rear 
edge  turned  up  so  that  the  general  wing  shape  is 
like  a  thin  letter  "S."  Such  wings  as  these  would 
not  tend  to  lose  their  proper  angle,  because  when  the 
angle  is  changed  for  any  reason  the  center  or  pres- 
sure in  these  wings  moves  in  just  the  manner  neces- 
sary to  restore  them  to  their  proper  position;  but 
these  wings  are  inefficient  and  are  not  in  present 
use  on  airplanes. 

The  Penaud  Tail  Principle.— Rule.— The  hori- 
zontal tail  must  have  a  smaller  angle  of  incidence 
than  the  wings.  The  upsetting  force  above  men- 


PRINCIPLES  OF  FLIGHT 


71 


tioned  must  be  met  by  a  strong  opposite  right- 
ing force,  and  this  latter  is  furnished  by  the  hori- 
zontal tail  surface.  In  the  angle  of  equilibrium  of 
2°  above  mentioned,  the  flat  horizontal  stabilizer  will 


LINE  OF 
LIFT- FORCE  " 


Lift behind 'center of 
gravity;  wing  -fends  to  dive. 


,, CENTER  OF 
.GRAVITY 


Lift  passes  through 

center  of  gravity ;  wincr 

is  balanced. 


15° 

Lift  ahead  of  center  of 
gravity;  wing  tends  to  rear  u ft 


INSTABILITY  OF  WING  WITH  NO  TAIL 
AFFIXED  TO  IT 


Downward  pressure  on  tail 
counteracts  diving  tendency. 


No  tail  pressure 
needed  for  balance. 


Upper  pressure  on  tail 
counteracts  rearing 

tendency. 
STABILITY  OF  WING  AND  TAIL  COMBINED 


rLINE 'OF 'LIFT-FORCE 


LONGITUDINAL  DIHEDRAL 
ANGLE 


FIG.  29. — Diagrams  illustrating  theory  and  application  of 
longitudinal  dihedral  angle. 

perhaps  have  no  force  acting  on  it  at  all  because  it 
is  edgewise  to  the  air  and  its  angle  of  incidence  is 
zero.  When  the  angle  of  the  wing  increases  to  2^° 
and  the  lift  moves  forward  tending  to  rear  it  up, 
the  wing  being  rigidly  fastened  to  the  body  pushes 


72  MANUAL  OF  AVIATION  PRACTICE 

the  tail  downward  so  that  the  tail  now  begins  to 
have  a  small  lift  force  upon  it  due  to  its  angle  of  y± ; 
and  this  newly  created  force,  though  small,  acts  at 
such  a  long  lever  arm  that  it  exceeds  the  rearing 
force  of  the  wing  and  will  quickly  restore  the  air- 
plane to  2°.  This  action  depends  upon  the  princi- 
ple of  the  Penaud  Tail  or  longitudinal  " Dihedral" 
which  requires  that  the  front  wings  of  an  airplane 
make  a  larger  angle  with  the  wind  than  the  rear 
surface.  This  principle  holds  good  even  when  we 
have  rear  surfaces  which  actually  are  lifting  sur- 
faces in  normal  flight,  the  requisite  being  that  the 
wings  themselves  shall  in  such  cases  be  at  an  even 
greater  angle  than  the  tail.  No  mention  .has  been 
made  of  the  elevator  control,  because  its  action  is 
additional  to  the  above-mentioned  stability.  The 
elevator  is  able  to  alter  the  lift  on  the  tail;  such 
alteration  requires,  of  course,  immediate  change  of 
angle  of  the  wings  so  that  equilibrium  shall  again 
follow;  and  th's  equilibrium  will  be  maintained  until 
the  lift  at  the  tail  is  again  altered  by  some  movement 
of  the  elevator  control.  Thus  the  elevator  may  be 
considered  as  a  device  for  adjusting  the  angle  of 
incidence  of  the  wings. 

The  air  through  which  the  wings  have  passed 
receives  downward  motion,  and  therefore  a  tail 
which Js  poised  at  zero  angle  with  the  line  of  flight 
may  actually  receive  air  at  an  angle  of  —  2°  or  —3°. 
In  the  above  case  we  would  expect  an  actual  down- 
ward force  on  the  tail,  unless  this  tail  is  given  a 
slight  arch  on  its  top  surface  (for  it  is  known  that 


PRINCIPLES  OF  FLIGHT  73 

arched  surfaces  have  an  angle  of  zero  lift  which  is 
negative  angle). 

Longitudinal  Control. — Steering  up  or  down  is 
done  by  the  elevator,  which  as  explained  above  is 
merely  a  device  for  adjusting  the  angle  of  incidence 
of  the  wings.  The  elevator  controls  like  all  the 
other  controls  of  an  airplane  depend  for  their  quick 
efficient  action  upon  generous  speed;  they  can  not  be 
expected  to  give  good  response  when  the  machine  is 
near  its  stalling  speed.  The  elevators  like  the 
rudder  are  located  directly  in  the  blast  of  the  pro- 
peller and  in  case  the  speed  of  motion  should  become 
very  slow,  the  elevators  may  be  made  to  exert  con- 
siderable controlling  force  if  the  motor  is  opened  up 
to  blow  a  strong  blast  against  them.  This  is  good 
to  bear  in  mind  when  taxying  on  the  ground  because 
if  the  motor  is  shut  off  at  the  slow  speed  of  motion 
the  elevator  and  rudder  will  lose  their  efficacy.  The 
propeller  blast,  due  to  a  25  per  cent,  slip,  adds  25 
per  cent,  of  apparent  speed  to  those  parts  which  are 
in  its  way,  and  therefore  the  tail  forces  are  affected 
as  the  square  of  this  increase,  that  is,  the  forces  may 
be  50  per  cent,  greater  with  the  propeller  on  than  off. 

Lateral  Stability. — This  depends  upon  the  keel 
surface  or  total  side  area  of  an  airplane.  The  keel 
surface  includes  all  the  struts,  wires,  wheels,  wings, 
as  well  as  body,  against  which  a  side  wind  can  blow. 
Skidding  and  side-slipping  have  the  same  effect  as  a 
side  wind,  and  the  resulting  forces  acting  against 
the  side  of  the  machine  should  be  made  useful 
instead  of  harmful.  This  is  done  by  properly 


74 


MANUAL  OF  AVIATION  PRACTICE 


proportioning  the  keel  or  side  surface.  If  keel  sur- 
face is  low,  the  side  force  will  rotate  the  airplane 
about  its  axis  so  that  the  windward  wing  sinks;  if 
high,  so  that  it  rises.  But  if  the  keel  surface  is  at 
just  the  right  height  (i.e.,  level  with  the  center  of 
gravity)  the  side  forces  will  not  rotate  the  machine 
at  all  and  will  simply  oppose  the  skidding  without 
upsetting  equilibrium. 


•r- DIHEDRAL  AN6LE 


FIG.  30.— Diagram  showing  effect  on  lateral  stability  of  dihedral 
angle  and  non-skid  fins. 

(a)  Machine  flying  level.  (6)  Machine  tips  and  side-slips:  excess  pressure  is 
created  on  windward  wing  and  fins,  (c)  Machine  has  side-slipped  and  rotated 
back  to  level. 

Lateral  Dihedral. — Now  when  an  airplane  ap- 
pears to  have  its  keel-surface  center  too  low,  the 
easiest  way  to  raise  it  level  with  the  center  of 
gravity  is  to  give  the  wings  a  dihedral  angle,  that  is 


PRINCIPLES  OF  FLIGHT  75 

make  them  point  upward  and  outward  from  the 
body.  Thus  their  projection,  as  seen  in  a  side  view, 
is  increased,  and  the  effect  is  to  add  some  keel  sur- 
face above  the  center  of  gravity,  thus  raising  the 
center  of  total  keel  surface. 

A  further  advantage  of  the  lateral  dihedral  is  that 
any  list  of  the  airplane  sideways  is  automatically 
corrected  (see  Fig.  30).  The  low  wing  supports 
better  than  the  high  wing,  because  a  side  slip  sets 
in,  hence  will  restore  the  airplane  to  level  position. 

Non -Skid -Fins. — Where  for  the  above-mentioned 
purposes  an  excessive  dihedral  would  be  needed, 
resort  may  be  had  to  non-skid-fins  erected  vertically 
edgewise  to  the  line  of  flight  above  or  beneath  the 
topwing.  These  are  used  in  marine  machines  to 
balance  the  abnormally  large  keel  surface  of  the 
boat  or  pontoon  below. 

Lateral  Control. — By  means  of  ailerons,  lateral 
control  is  maintained  voluntarily  by  the  pilot; 
the  aileron  on  the  low  tip  is  given  a  greater  angle  of 
incidence  while  on  the  high  tip  a  less  angle  of 
incidence  thus  restoring  the  proper  level  of  the 
machine.  Notice  that  the  efficacy  of  the  ailerons 
depends  upon  speed  of  motion  of  the  airplane,  irre- 
spective of  propeller  slip  because  the  propeller  slip 
does  not  reach  the  ailerons.  Therefore,  at  stalling 
speeds  the  ailerons  may  not  be  expected  to  work  at 
their  best,  and  when  lateral  balance  is  upset  at 
slow  speeds  it  is  necessary  to  dive  the  machine 
before  enough  lateral  control  can  be  secured  to 
restore  the  balance. 


76  MANUAL  OF  AVIATION  PRACTICE 

Directional  Stability. — Directional  stability  has 
to  do  with  the  tendency  of  an  airplane  to  swerve  to 
the  right  or  left  of  its  proper  course.  To  maintain 
directional  stability  the  " vertical  stabilizer"  is  used, 
which  acts  in  a  manner  analogous  to  the  feather  on 
an  arrow.  Thus  in  case  of  a  side  slip  the  tail  will 
swing  and  force  the  airplane  nose  around  into  the 
direction  of  the  side  slip  so  that  the  airplane  tends 
to  meet  the  relative  side  wind  " nose-on"  as  it 
should.  The  vertical  stabilizer  should  not  be  too 

ELEVATORS;    .      ^  (RUDDER 
AILERON— \ 


'WHEEL  (Moves *„*,  v, ^     . 
M^ 


WHEEL  COLUMN      . 
(Moves  Elevators) 

-FOOT  BAR  (Moves  Rudder) 
FIG.  31.— Deperdussin  control. 
System  used  in  U.  S.  training  airplanes. 

large,  however,  as  then  any  side  pressure  due  to 
deviation  from  a  rectilinear  course  will  cause  the 
machine  to  swerve  violently;  the  wing  which  is  out- 
ermost in  the  turn  will  have  preponderance  of  lift 
due  to  its  higher  speed;  that  is,  the  airplane  will  get 
into  a  turn  where  there  is  too  much  bank  and  a  spiral 
dive  may  result. 


PRINCIPLES  OF  FLIGHT  77 

Directional  Control. — The  rudder  gives  direc- 
tional control  in  exactly  the  same  way  that  it  does 
on  a  boat;  it  should  be  said,  however,  that  the  rudder 
is  sometimes  used  without  any  intention  of  changing 
the  direction,  that  is,  it  is  used  simultaneously  with 
the  ailerons  as  a  means  of  neutralizing  their  swerv- 
ing tendency.  The  ailerons,  of  course,  at  the  same 
time  that  they  restore  lateral  balance  create  a  dis- 
advantageous tendency  to  swerve  the  machine 
away  from  its  directional  course;  that  is  what  the 
rudder  must  neutralize.  Moreover,  the  rudder  is 
frequently  used  against  side  winds  to  maintain  rec- 
tilinear motion. 

Banking. — Banking  combines  the  lateral  and 
directional  control,  which  should  be  operated  simul- 
taneously so  as  to  tilt  the  machine  and  at  the  same 
time  maintain  the  radius  of  turn.  The  wings  are 
tilted  in  a  bank  because  in  going  around  a  curve  of  a 
certain  radius  the  weight  of  the  machine  creates  a 
centrifugal  force  in  a  horizontal  direction  and  if  the 
curved  path  is  to  be  maintained  this  centrifugal 
force  must  be  neutralized;  and  this  is  done  by  in- 
clining the  force  of  lift  inward  until  it  has  a  hori- 
zontal component  equal  to  the  centrifugal  force. 
That  is  why  the  angle  of  bank  must  be  rigidly  ob- 
served, or  else  the  inward  component  of  the  lift 
will  change.  Now  as  soon  as  the  wings  bank  up,  the 
lift Jforce  is  no  longer  all  vertical  and  therefore  may 
not  be  enough  to  support  the  weight  of  the  machine. 
To  offset  this  have  plenty  of  motor  power  for  speed 
in  a  bank;  and  do  not  try  to  climb  while  banking. 


78  MANUAL  OF  AVIATION  PRACTICE 

It  is  better  to  bank  too  little  than  too  much;  too 
little  results  in  skidding  which  may  be  easily  cured; 
too  much  results  in  side  slipping  inward  and  if  the 
tail  surface  is  too  great  in  this  latter  case,  a  spiral 
dive  may  result — so  look  out  for  overbanking. 

It  is  better  for  the  beginner  in  banking  to  move 
his  ailerons  first  and  then  move  the  rudder;  for  if  he 
moves  the  rudder  first  there  will  be  skidding  out- 
ward, forward  speed  will  drop  and  a  stall  may 
result.  On  high  angles  of  banking,  over  45°,  it 
should  be  noted  that  the  elevators  are  now  more 
nearly  vertical  than  horizontal  and  operate  as  a 
rudder;  similarly  the  rudder's  function  is  reversed, 
and  to  turn  down  the  rudder  will  be  used. 

Damping  in  an  Airplane. — Above  have  been  men- 
tioned the  restoring  forces  which  tend  toward  air- 
plane equilibrium.  Now  these  restoring  forces 
tend  to  push  the  machine  back  to  equilibrium  and 
even  beyond  in  exactly  the  same  way  that  gravity 
causes  a  pendulum  to  swing  about  its  point  of  equi- 
librium. This  can  sometimes  be  noticed  in  the  case 
of  an  automobile  when  travelling  at  high  speed  along 
country  roads  where  a  sort  of  slow  oscillation  from 
side  to  side  may  be  noticed  due  to  the  forceful  main- 
tenance of  equilibrium  of  the  body  in  its  forward 
motion.  This  oscillation  in  an  airplane  would  be 
serious  unless  there  were  means  of  damping  it  out 
and  these  means  are:  first,  the  wings;  second,  the 
tail  surfaces;  third,  the  weight  and  inertia  of  the 
machine  itself.  Regarding  inertia  it  should  be 
said  that  a  machine  with  weight  distributed  far 


PRINCIPLES  OF  FLIGHT  79 

from  the  center  of  gravity,  such  as  the  double- 
motor  airplane  has  a  large  tendency  to  resist  the 
rolling  motions  associated  with  lateral  stability. 
But  from  the  same  sign  airplanes  with  large  moment 
of  inertia  are  difficult  to  deviate  from  any  given 
attitude,  and  therefore  have  the  name  of  being 
"logy. "  The  proper  proportioning  of  an  airplane's 
parts  to  secure  first,  the  restoring  forces;  second,  the 
proper  damping  force;  third,  the  proper  amount  of 
moment  of  inertia,  is  a  very  delicate  matter  and 
beyond  the  scope  of  the  present  chapter. 


CHAPTER  IV 
FLYING  THE  AIRPLANE 

Starting  Off. — The  first  thing  to  do  before  start- 
ing off  in  an  airplane  is  to  inspect  carefully  every- 
thing about  the  machine  and  assure  yourself  that 
it  is  in  perfect  condition. 

When  all  is  ready  to  start  turn  the  machine 
directly  against  the  wind;  this  is  done  in  order  that 
the  rise  from  the  ground  may  be  more  quickly  made 
with  the  assistance  of  the  wind  under  the  wings, 
and  it  has  a  more  important  advantage  in  the  fact 
that  if  you  try  to  get  off  the  ground  across  the  wind 
the  machine  will  be  very  hard  to  balance.  Birds 
also  take  the  air  directly  against  the  wind  even 
though  for  the  moment  this  carries  them  in  a  direc- 
tion toward  some  supposed  enemy,  and  it  is  a 
fundamental  principle  in  airdromes.  Keep  the 
machine  pointed  into  the  wind  for  the  first  200  ft. 
of  altitude  (and  similarly  in  landing  face  the  wind 
when  within  200  feet  of  the  ground).  In  case  the 
engine  should  fail  before  a  height  of  200  ft.  is 
reached,  never  turn  down  wind  as  this  is  extremely 
dangerous. 

Assistance   will   be  had   for  the  start  from  the 
mechanics,  or  if  away  from  the  airdrome  from  by- 

80 


FLYING  THE  AIRPLANE 


81 


standers.  Have  each  assistant  in  his  proper  place 
before  starting  the  engine;  one  is  to  start  the 
propeller  and  the  rest  to  hold  back  the  machine 
until  ready  to  let  go. 

In  order  to  get  off  the  ground  you  will  want  good 
engine    power;    it    takes    considerable    thrust    to 


(From  "How  to  Instruct  in  Flying.") 

FIG.  32. — Airplane  in  flying  position  just  after  starting. 

This  cut  also  illustrates  proper  landing  attitude,  since  airplane  is  just 

skimming  the  ground. 

accelerate  an  airplane  on  the  ground  to  its  flying 
speed;  in  fact  the  first  flying  machine  of  the  Wrights 
had  to  use  an  auxiliary  catapult  to  furnish  the 
thrust  necessary  to  get  them  into  the  air.  Mak- 
ing sure  that  the  motor  is  giving  full  power  raise  the 
hand  as  a  signal  to  the  attendants  to  remove  the 
chocks  and  let  go.  As  you  start  rolling  forward 


82  MANUAL  OF  AVIATION  PRACTICE 

push  the  control  lever  forward  which  will  raise  the 
tail  off  the  ground  and  place  the  wings  edgewise 
to  the  wind  while  they  will  not  offer  resistance  to 
the  acquiring  of  good  rolling  speed.  Within  a  few 
seconds  the  machine  will  have  attained  on  the 
ground  a  velocity  not  less  than  the  low  flying  speed; 
it  will  not  rise,  however,  until  the  tail  is  lowered 
by  pulling  the  lever  back.  When  the  necessary 
rolling  speed  is  attained  pull  the  lever  softly  back- 
ward; the  tail  at  once  drops,  the  wings  increase 
their  angle  and  lift  and  the  machine  will  rise,  the 
lever  being  held  in  a  fixed  position  (see  Fig.  32). 
The  distance  between  the  point  of  starting  and  ris- 
ing will  be  100  yd.  or  more  and  will  occupy  from 
5  to  10  sec.  depending  on  the  wind. 

The  change  from  flying  position  to  climbing  posi- 
tion is  only  a  slight  modification  involving  only  a 
slight  pulling  back  of  the  control  lever  and  holding 
it  in  fixed  position;  the  motor  may  in  some  machines 
simply  be  opened  out  when  its  increased  power  will 
make  the  machine  rise;  however,  there  is  only  one 
speed  at  which  the  climb  will  be  fastest  and  there- 
fore it  is  well  to  know  what  is  the  proper  speed 
for  climbing;  the  motor  is  then  opened  out  full 
and  the  airplane  operated  to  give  the  proper  speed 
corresponding. 

The  pupil  should  rise  to  the  height  of  at  least  100 
ft.,  as  any  less  is  useless  and  nothing  will  be  learned 
from  landing.  In  the  case  of  cross-country  flying 
the  pilot  will  rise  to  the  height  of  2000  ft.,  circling 
over  the  field  rather  than  flying  off  in  a  straight 


FLYING  THE  AIRPLANE 


83 


line  so  that  preparatory  to  his  start  he  always  has 
the  flying  field  in  reach. 

Landing. — Proper  landing  is  the  most  important 
thing  in  airplane  flying.  The  pilot  in  turning  his 
machine  downward  toward  a  landing  spot  from 
flight  will  choose  a  distance  from  the  field  equivalent 


(From  "  How  to  Instruct  in  Flying. ") 

FIG.  33. — Airplane  in  gliding  position,  approaching  a  landing. 

Note  that  its  attitude  relative  to  line  of  flight  is  similar  to  "  flying  position," 

line  of  flight  however  being  inclined. 

to  the  proper  gliding  angle  of  his  machine.  If  the 
gliding  angle  is  1  in  7  he  must  not  turn  downward 
any  further  from  the  field  than  a  distance  greater 
than  seven  times  his  altitude  or  he  will  fall  short. 
It  is  safer  to  come  closer  to  the  field  before  turning 
downward  for  two  reasons:  first,  because  you  may 


84  MANUAL  OF  AVIATION  PRACTICE 

not  be  gliding  at  the  best  gliding  angle;  second, 
because  you  can  always  kill  extra  height  by  a  spiral 
or  two  better  than  you  can  regain  it.  Have  height 
to  spare  when  landing. 

To  come  down  throttle  down  the  engine  and  push 
the  lever  softly  forward  until  the  proper  gliding  angle 
is  obtained  (Fig.  33).  The  reason  for  throttling 
down  the  engine  is:  first,  that  you  do  not  need  its 
thrust  when  you  are  coasting  down  because  gravity 
furnishes  all  the  necessary  velocity;  second,  if  you 
glide  or  dive  with  the  motor  wide  open  high  speed 
will  result,  resulting  in  strains  on  the  machine  es- 
pecially on  the  moment  of  leveling  out  again;  third, 
at  this  high  speed  the  controls  become  stiff  -to 
operate. 

Maintain  the  proper  gliding  speed  to  within  5 
miles  an  hour  of  what  it  ought  to  be  as  it  is  the  speed 
which  determines  the  proper  gliding  angle.  The 
revolution  counter  will  indicate  what  the  speed  is 
or  the  air-speed  meter  may  be  used.  Arrange  to 
come  on  to  the  field  facing  directly  into  the  wind, 
which  may  be  observed  by  watching  smoke  or 
flags  below.  In  landing  against  the  wind  you  are 
again  copying  the  practice  of  the  birds.  When  you 
come  to  within  15  ft.  of  the  ground  pull  the  lever 
softly  back  until  the  machine  is  in  its  slow-flying 
position,  which  should  be  attained  5  ft.  above  the 
ground  (Fig.  34).  Hold  the  stick  at  this  position  of 
horizontal  flying;  no  further  movement  of  the  lever 
is  necessary  except  to  correct  bumps,  for  which 
purpose  it  would  be  held  lightly  for  instant  action. 


FLYING  THE  AIRPLANE 


85 


86  MANUAL  OF  AVIATION  PRACTICE 

The  aileron  control  must  be  used  here  to  keep  the 
machine  level  and  it  may  be  necessary,  to  operate 
the  rudder  after  touching  the  ground  in  order  to 
avoid  swerving;  in  fact  some  machines  are  provided 
with  a  rear  skid  which  steers  for  this  purpose. 

In  rolling  just  after  landing  keep  the  tail  as  close 
to  the  ground  as  possible  without  causing  undue 
bumping,  so  that  the  maximum  resistance  of  the 
wings  may  be  presented  to  the  air  and  the  machine 
be  slowed  up  rapidly.  Some  machines  are  fitted 
with  brakes  on  the  wheels  to  assist  in  the  quick 
retardation  of  the  roll.  Landing  is  one  of  the  biggest 
problems  in  aviation  and  is  a  hard  thing  to  learn 
because  it  is  done  at  a  high  speed  especially  in  the 
fast  military  machines  such  as  the  Fokker,  Nieu- 
port,  etc.  Landing  is  more  of  a  problem  than  it 
used  to  be  in  the  early  days  when,  for  instance,  the 
Wrights  were  able  to  land  without  any  wheels  at 
all  on  mere  skids  because  their  machines  were  not 
fast. 

The  following  are  examples  of  bad  landings : 

1.  The  pancake  results  from  allowing  the  machine 
to  get  into  its  rising  position  when  it  is  landing 
(Fig.  35).     There  will  be  a  perpendicular  bounce 
and  on  the  second  bounce  the  running  gear  will 
break.     In  order  to  get  out  of  an  immanent  pan- 
cake open  up  the  engine  to  keep  machine  flying, 
put  the  machine  into  a  flying  position,  then  throttle 
down  again  and  land. 

2.  Another  type  of  pancake  results  from  bring- 
ing the  machine  out  of  its  gliding  position  at  a  point 


FLYING  THE  AIRPLANE 


87 


too  far  above  the  ground  when  the  machine  will 
drop  due  to  lack  of  speed  and  break  the  running 
gear.  To  avoid  this  open  motor  full,  thus  regaining 
speed  and  flying  position;  afterward  throttle  down 
and  reland. 


(From  "  How  to  Instruct  in  Flying.") 

FIG.  35. — Bad  landing,  Type  1 — the  "pancake"  landing. 

Line  of  flight  is  downward;  angle  of  incidence  large,  hence  speed  is  slow;  but 

there  is  too  much  downward  momentum  and  landing  gear  will  break.     Should 

line  of  flight  arrow  point  upward,  airplane  as  shown  would  then  be  in  climbing 

position. 


3.  A  third  type  of  bad  landing  results  from  failure 
to  turn  the  machine  out  of  its  glide  at  all,  so  that  it 
glides  straight  downward  until  it  touches  the  ground. 
This  is  the  most  dangerous  case  of  all  the  bad  land- 
ings. To  cure  it  open  up  the  engine  after  the  first 


88  MANUAL  OF  AVIATION  PRACTICE 

bounce,  regaining  flying  speed  before  the  second 
bounce;  then  reland. 

4.  If  at  the  moment  of  landing  the  rudder  is 
turned  causing  machine  to  swerve,  or  if  the  machine 
is  not  level,  a  side  strain  will  be  placed  upon  the 
landing  gear  and  the  wheels  will  buckle  (Fig.  36). 


(From  "How  to  Instruct   in  Flying.  ") 
FIG.  36. — Bad  landing  Type  4 — machine  not  level. 
Wheels  do  not  touch  ground  at  same  time,  and  one  may  smash. 


CHAPTER  V 
CROSS-COUNTRY  FLYING 

Cross-country  flying  differs  from  ordinary  air- 
drome flying  in  that  it  takes  you  a  long  way  off  from 
your  landing  field.  On  the  airdrome  your  chief 
anxiety  is  to  learn  how  to  fly,  how  to  work  the 
controls,  how  to  bank;  but  in  cross-country  work, 
you  are  supposed  to  have  all  the  technique  of  air- 
plane operation  well  in  hand,  so  that  you  do  not 
have  to  think  much  about  it.  In  cross-country 
flying,  then,  your  chief  anxiety  will  be  to  arrive 
at  your  destination  and  to  be  constantly  searching 
out  available  landing  fields  in  case  of  engine  failure. 
The  first  cross-country  flight  you  make  may  be  a 
short,  easy  one,  in  which  there  are  plenty  of  avail- 
able landing  places,  and  on  which  you  will  be  able 
to  make  a  regular  reconnaissance  report.  Further 
experience  in  cross-country  work  will  involve  more 
and  more  difficult  trips,  until  you  will  think  nothing 
of  flying,  for  example,  on  long  raiding  tours  over 
unfamiliar  enemy  country. 

Equipment. — Knowing  that  you  may  have  to  land 
far  away  from  any  headquarters,  you  must  take  a 
complete  set  of  tools  and  covers  for  the  airplane. 
Your  clothing  need  not  be  different  from  usual,  and 
will  comprise  helmet,  goggles,  leather  suit,  and 


90  MANUAL  OF  AVIATION  PRACTICE 

gloves.  Do  not  forget  your  handkerchief,  which 
you  frequently  need  to  clean  off  your  goggles. 

The  instruments  needed  on  a  cross-country  trip 
are:  a  compass,  which  should  be  properly  adjusted 
before  starting  and  the  variation  angle  noted. 
A  wrist  watch  is  necessary;  ordinary  dashboard 
clocks  go  wrong  on  account  of  the  'vibration. 
Take  an  aneroid  barometer  with  adjustable  height 
reading.  Of  course  you  will  depend  upon  a  revolu- 
tion indicator,  for  no  matter  how  experienced  a 
pilot  may  be  in  " listening  out"  faulty  engine 
operation,  after  a  long  flight  his  ear  loses  its  acute- 
ness,  and  he  will  fall  back  on  the  revolution  indi- 
cator for  assistance.  The  air-speed  meter,  whether 
of  the  Pitot  type  or  pressure-plate  type,  will  prove 
invaluable  in  flying  through  clouds  or  mist  when  the 
ground  is  obscured.  Also  the  inclinometer  is 
able  to  give  the  angle  of  flight  when  the  earth  is 
not  visible,  although  the  speed  indicator  usually  is 
sufficient  to  give  the  angle  of  flight,  for  an  increase 
of  speed  means  downward  motion  and  decrease  of 
speed  means  upward  motion.  Additional  instru- 
ments may  be  used. 

Map. — The  map  is  essential  for  cross-country 
work.  It  should  be  tacked  on  to  the  map  board  if 
the  flight  is  short,  but  made  to  run  on  rollers  if  the 
flight  is  long.  In  the  latter  case  the  map  is  in  the 
form  of  a  single  long  strip,  while  your  flight  may  be 
full  of  angles;  therefore  you  will  have  to  practice 
using  this  sort  of  map,  in  which  the  corners  of 
your  flight  are  all  drawn  as  straight  lines.  The 


CROSS-COUNTRY  FLYING  91 

scale  of  maps  may  be  2  or  4  miles  to  the  inch  for 
long  flights.  This  scale  is  sometimes  spoken  of 
as  a  fractional  figure;  that  is,  2  miles  to  the  inch  is 
the  same  as  K27>ooo  scale.  The  map  should  be 
studied  most  carefully  before  the  start  of  the  trip. 
The  course  which  you  propose  to  fly  should  be 
marked  out  on  it;  all  available  landmarks  which 
could  be  of  service  as  guides  should  be  distinctly 
noticed  and  marked  on  the  map  where  necessary. 
These  landmarks  will  in  case  there  is  no  wind  enable 
you  to  make  your  trip  without  using  the  compass  at 
all,  and  in  case  of  wind,  are  essential  as  a  check  on 
the  compass.  Mark  off  the  distance  in  miles  be- 
tween consecutive  points  of  your  course..  Mark  the 
compass  bearing  of  each  leg  of  this  course. 

As  landmarks  towns  are  the  best  guides,  and  they 
should  be  underscored  on  the  map,  or  enclosed  in 
circles.  It  is  customary  not  to  fly  actually  over 
towns.  Railways  are  very  good  assistance  to  find- 
ing your  way,  and  these  should  be  marked  on  the 
map  in  black  wherever  they  approach  within  10 
miles  of  the  course.  Mark  water  courses  with  blue 
color,  and  roads  with  red. 

Landmarks. — Only  practice  can  make  a  pilot 
good  at  observing  the  various  features  of  the  ground 
beneath  him.  The  various  features  which  can  be 
used  as  guides  are  those  which  are  most  visible. 
After  towns,  railways  come  next  in  importance. 
Their  bridges,  tunnels,  etc.,  make  good  landmarks. 
On  windy  days  when  relying  on  the  compass,  it  will 
be  well  to  keep  in  sight  of  a  railway  even  if  this  be 


92  MANUAL  OF  AVIATION  PRACTICE 

the  longer  way  around,  because  the  railway  gives  a 
constant  check  upon  the  compass  bearing.  In  this 
case  you  will  have  noted  on  your  map  a  general 
magnetic  bearing  of  the  railway,  which  bearing  you 
can  readily  compare  with  your  compass  reading. 
Moreover,  the  railway  is  good  in  case  you  become 
involved  in  a  fog  or  mist  for  a  time.  It  should  be 
remembered,  however,  that  on  most  of  the  maps  no 
distinction  is  made  between  one  and  two-track 
roads;  also  that  it  is  easy  to  make  mistakes  where 
branch  lines  are  not  shown  on  the  map  because  they 
are  dead  ends  leading  to  private  quarries,  etc.,  and 
may  be  taken  for  junctions.  Railways  sometimes 
seem  to  end  abruptly,  which  means  that  you  are 
looking  at  a  tunnel. 

Water  is  visible  from  a  great  distance.  Cautions 
to  be  observed  are  that  after  a  heavy  rain  small 
flooded  streams  may  take  on  the  appearance  of 
larger  bodies  of  water  or  lakes,  which  you  will  have 
difficulty  in  reconciling  with  the  map.  Small  rivers 
are  often  overhung  with  foliage,  and  to  follow  them 
in  all  their  curves  will  waste  a  lot  of  time. 

The  use  of  roads  as  guides  may  be  governed  by 
the  fact  that  paved  roads  are  usually  main  roads, 
and  telegraph  wires  may  be  expected  along  them. 
In  the  newer  parts  of  the  United  States  the  system 
of  laying  out  roads  provides  a  very  useful  means 
of  gaging  distances;  I  refer  to  the  section  system 
which  is  in  use,  for  instance,  in  Illinois,  where  there 
is  a  road  every  mile  running  north  and  south,  so 
that  the  entire  country  is  cut  up  into  squares  1 


CROSS-COUNTRY  FLYING  93 

mile  on  each  side,  with  occasional  roads  of  course  at 
i^-mile  and  i^-mile  points. 

Navigation  by  Landmarks. — In  all  cases  of  cross- 
country flying  the  pilot  will  have  two  independent 
systems  of  maintaining  his  proper  directions:  first, 
the  computed  compass  bearing;  second,  the  use  of 
landmarks  whose  position  is  known.  In  comparing 
his  computed  course  with  the  course  actually  indi- 
cated by  passing  over  these  landmarks  the  rule 
should  be  made  that,  in  case  of  doubt  when  a  land- 
mark is  not  distinctly  recognized,  take  the  compass 
course;  there  are  many  chances  that  a  landmark 
may  be  altered  or  even  removed  without  being  so 
recorded  on  the  pilot's  map,  whereas  the  errors  of 
the  compass  of  course  are  presumably  understood 
by  the  pilot  who  has  secured  every  opportunity  to 
check  it  when  passing  previous  landmarks. 

It  is  important  to  note  the  time  of  completing 
successive  stages  of  the  flight,  that  is  when  passing 
over  predetermined  landmarks.  Time  is  a  very 
uncertain  condition  to  ascertain  in  airplane  flying 
for  it  seems  to  pass  quickly  on  calm  days  but  slowly 
when  the  journey  is  rough.  If  the  pilot  does  not 
check  the  time  interval  betwreen  successive  objects 
he  is  quite  likely  to  expect  the  next  before  it  is  really 
due. 

Landing  Fields. — Next  to  the  ever-present  worry 
which  the  pilot  has  regarding  the  perfect  operation 
of  his  engine,  the  most  important  thing  about  cross- 
country flying  is  that  wherever  he  may  be  he  must 
have  available  a  landing  field  within  gliding  dis- 


94  MANUAL  OF  AVIATION  PRACTICE 

tance  in  case  his  engine  defaults.  The  question  is  of 
course  immediately  raised,  "What  if  there  is  no 
landing  field  within  gliding  range?"  The  answer 
to  this  is  that  the  pilot  will  instinctively  learn  to 
keep  his  eyes  open  for  landing  possibilities  every 
minute  of  his  progress  whether  he  expects  to  use 
them  or  not ;  in  cross-country  flying  the  lookout  for 
fields  is  first  and  foremost  in  his  mind;  if  there  are 
no  fields,  it  is  up  to  him  to  pick  out  a  spot  of  ground 
which  is  the  least  objectionable  for  a  landing.  In 
the  State  of  Illinois  the  question  of  landing  fields  is 
almost  non-existent,  because  there  are  large,  flat 
fields  and  pastures  in  almost  every  square  mile  of 
the  farming  district,  and  a  cross-country  flight  from 
Rantoul  to  Chicago  could  have  no  terrors  for  the 
beginner  as  regards  the  choice  of  a  landing  ground. 
When  it  comes  to  a  cross-country  flight  like 
Ruth  Law's,  from  Chicago  to  New  York,  these 
favorable  conditions  begin  to  disappear  after  the 
middle  of  the  journey,  that  is,  east  of  Buffalo.  The 
most  ideal  condition  for  cross-country  flying  would 
be  one  like  that  on  the  London-Edinburgh  route, 
where  landing  grounds  are  so  frequent  that  by  flying 
at  a  height  of  a  couple  of  miles  the  pilot  can  free  his 
mind  completely  of  the  worry  of  suitable  landing 
places;  but  in  the  United  States  we  have  very  few 
established  airdromes,  and  the  only  approach  to 
the  London-Edinburgh  route  is  the  St.  .Louis-New 
York  route,  where  the  jumps  are  approximately 
150  miles;  namely,  St.  Louis,  Champaign,  Indian- 
apolis, Dayton,  Sandusky,  Erie,  Hammondsport, 


CROSS-COUNTRY  FLYING  95 

Philadelphia,  and  New  York.  That  is  why  long 
cross-country  trips  are  such  an  adventure  in  this 
country  and  such  an  ordinary  affair  in  England. 

The  beginner  will  have  special  difficulty  in  train- 
ing his  mind  to  pick  out  available  landing  places; 
first  of  all  because  the  earth  looks  so  different  from 
the  sky  that  it  is  only  with  practice  a  beginner  learns 
the  shades  and  hues  of  color  which  mean  certain 
kinds  of  ground,  or  learns  to  spot  the  different  fea- 
tures of  flat  and  hilly  country.  Even  for  an  ac- 
complished pilot  it  is  hard  to  tell  whether  a  field 
is  good  or  bad  from  a  height  of  over  1000  ft. ;  and  as 
it  is  dangerous  to  fly  this  low  over  unknown  terri- 
tory, you  can  at  once  see  what  is  meant  by  the 
worry  of  scanning  the  countryside  for  available 
fields. 

Choose  the  best  field  that  you  can  get,  having  a 
smooth  surface  and  being  easy  to  get  out  of  in  all 
directions.  The  following  considerations  are  in- 
tended as  a  guide  to  what  constitute  the  best 
field,  in  case  you  have  a  choice  between  several 
possibilities. 

1.  Choose  a  field  near  a  town  if  possible,  or  failing 
that,  near  a  main  road  or  at  least  a  good  road. 
Remember  that  a  field  which  appears  to  be  near  a 
town  from  the  air  may  actually  turn  out  to  be  a  long 
walk  after  you  have  landed  there  and  find  that  there 
are  various  trips  to  be  made  to  and  fro  between  your 
chosen  landing  spot  and  the  town  for  the  purpose  of 
securing  ropes,  gasoline,  supplies,  etc.  If  you  land 
near  a  main  road  there  will  probably  be  telegraph 


96  MANUAL  OF  AVIATION  PRACTICE 

wires  along  it,  which  are  undesirable  in  the  case  of  a 
small  field  and  wind  direction  such  that  you  have 
to  rise  off  the  field  over  the  telegraph  wires.  It  is 
often  hard  to  distinguish  between  main  roads  and 
minor  roads,  and  it  will  be  wise  to  look  for  the  num- 
ber of  vehicles  on  any  road  in  determining  whether 
or  not  it  is  the  main  road. 

2.  The  best  field  is  a  stubble  field,  and  is  most 
numerous  of  course  in  the  fall  when  the  crops  are  in. 
It  will  have  a  lightish  brown  color  when  seen  from  a 
height,  and  is  pretty  sure  to  be  smooth,  without 
ditches  or  mounds.     Grass  land  is  next  best,  but  is 
often  full  of  mounds.     Plowed,  furrow  fields  are  to 
be  avoided.     It  might  be  said  that  stubble  fields 
will  be  hard  to  get  out  of  after  a  wet  night.     Vege- 
table and  corn  fields  have  a  dark  green  appearance 
which  the  pilot  must  learn  to  distinguish  from  grass 
pastures,  etc.     If  you  choose  pasture  land,  remem- 
ber that  in  summer  evenings  the  farm  animals  will 
generally  be  lying  down  near  the  hedges. 

3.  Avoid  river  valleys  for  landing  over  night,  as 
there  is  liable  to  be  a  fog  in  the  morning.    . 

4.  Any  field  which  has  been  previously  used  for 
landing  with  success  by  an  army  officer  can  be 
wisely  chosen. 

The  final  determination  of  landing  field  character- 
istics can  be  made  when  your  airplane  has  descended 
to  a  height  of  1000  ft.  off  the  ground,  and  in  case 
you  are  not  making  a  forced  landing  and  your  en- 
gine is  still  going,  you  can  check  up  your  estimate  by 
descending  to  this  level. 


CROSS-COUNTRY  FLYING  97 

Proper  Dimensions  of  Fields  and  Airdromes. — 
There  are  three  kinds  of  flying  fields.  One  is  the 
airdrome  which  is  used  exclusively  for  flying,  and 
may  be  as  large  as  a  mile  square;  very  few  of  these 
will  be  found  in  cross-country  flights  in  the  United 
States.  Second,  there  is  what  is  called  the  "  one- 
way" field,  a  long,  narrow,  open  space  which  is  us- 
able when  the  wind  blows  parallel  to  its  length. 
Third,  there  is  the  "two-way"  field,  which  has  two 
sufficiently  long  runways  at  right  angles  to  each 
other.  A  two-way  field  is  very  much  better  than  a 
one-way  field,  inasmuch  as  you  can  always  head 
within  45°  of  the  wind,  whereas  in  a  one-way  field 
an  extreme  case  would  be  90°.  Moreover,  two-way 
fields,  such  as  the  crescent-shaped  field  at  Dayton, 
Ohio,  sometimes  permit  of  almost  universal  direc- 
tion of  flight.  The  two-way  field  may  be  crescent- 
shaped,  T-shaped,  or  L-shaped.  An  L-shaped  field 
should  have  each  arm  200  by  300  yd.  Under  cer- 
tain conditions  there  may  be  buildings  located  in- 
side or  outside  the  angle  which  do  no  harm  aside 
from  creating  eddies  in  case  of  strong  wind.  A 
T-shaped  field  should  also  have  its  arms  300  by  200 
yd.  in  size. 

Regarding  the  size  of  fields  it  can  be  said  that, 
while  the  JN-4  machine  will  rise  off  the  ground 
after  a  run  of  100  yd.  or  so,  a  field  of  this  length 
is  of  course  not  big  enough  for  frequent  use, 
especially  if  bordered  by  trees,  telegraph  lines, 
fences,  and  so  forth.  A  field  for  temporary  use 
should  be  at  least  200  by  200  yd.,  about  9  acres. 


98  MANUAL  OF  AVIATION  PRACTICE 

If  obstructions  at  the  edges  are  more  than  5  ft.  high 
add  to  this  200  yd.  a  distance  equal  to  twelve  times 
the  height  of  the  obstruction.  For  a  permanent 
field  300  yd.  is  the  minimum  dimension  necessary 
for  clearing  obstacles  and  must  be  increased  if  the 
trees  exceed  50  ft.  in  height.  This  minimum  dimen- 
sion assumes  hard  ground  and  the  possibility  of 
starting  in  any  direction.  Training  fields  are  % 
mile  square  or  more. 

Whatever  field  is  used  either  temporarily  or 
permanently  by  the  pilot  should  be  absolutely 
familiar  to  him  over  every  inch  of  its  surface.  The 
adjacent  country  should  also  be  absolutely  familiar 
to  him  from  the  standpoint  of  possible  forced  land- 
ings which  he  may  have  to  make  during  his  flight; 
he  should  make  a  habit  of  informing  himself  as  to  all 
the  woods  and  hills,  etc.,  which  can  affect  air  currents 
in  the  neighborhood  of  the  field  from  which  he  is 
going  to  start. 

Guide  Posts  on  Airdromes. — Some  fields  have 
pot  holes  in  them,  and  these  holes  should  be  marked 
in  each  case  with  a  large  high  red  or  yellow  flag. 
Do'not  use  short,  small  flags,  as  they  will  frequently 
be  invisible  to  pilots  taxying  on  the  ground.  All 
telephone  wires,  etc.,  should  have  large  blankets  or 
other  suitable  signals  hung  over  them  to  warn  the 
pilot  away. 

Commonly  accepted  marks  for  designating  a  land- 
ing spot  on  airdromes  are  as  follows: 

For  day  use  a  large  letter  "T"  lying  on  the 
ground,  made  out  of  white  cloth  strips  15  by  3  ft. 


CROSS-COUNTRY  FLYING  99 

This  letter  T  is  shifted  with  the  wind  so  that  its 
long  leg  always  points  in  the  direction  of  the 
wind  and  the  pilot  will  therefore  have  nothing  to  do 
in  landing  but  approach  the  letter  "T"  from  the 
bottom,  so  to  speak. 

For  night  flying  a  system  of  four  flares  is  used,  so 
arranged  that  the  pilot  in  making  a  proper  landing 
will  pass  flare  A  on  his  left;  within  50  yd.  further 
on,  flare  B;  then  100  yd.  further  on,  flare  C,  also  on 
his  left.  In  passing  flare  C  he  will  have  a  fourth 
flare,  D,  50  yd.  to  his  right.  That  is  to  say,  the 
four  flares  make  the  outline  of  a  letter  "L"  and  the 
pilot  approaches  the  letter  UL"  having  the  long  leg 
on  his  left.  The  flares  may  be  made  by  putting 
half  a  gallon  of  gasoline  into  a  pail.  This  will 
burn  for  30  min.  and  will  be  visible  8  miles  away. 
Sometimes  at  night  instead  of  flares  white  sheets 
can  be  spread  on  the  ground  and  a  shaded  lamp  used 
to  illuminate  the  sheets. 

All  searchlights  on  the  landing  field  should  point 
in  the  direction  of  landing.  All  other  lights  within 
a  distance  of  a  mile  should  be  extinguished,  and  red 
lamps  should  be  used  at  danger  points. 

On  moonlight  nights  the  same  signals  and  guides 
may  be  used  as  in  the  daytime. 

Pegging  Down  an  Airplane. — In  landing  for  the 
night  do  not  stay  up  until  it  gets  dark  but  choose  a 
landing  place  which  will  allow  you  to  come  down  1  hr. 
before  dark;  this  amount  of  time  will  be  needed  for 
laying  up  the  machine  over  night.  As  you  come  to 
the  landing  ground  note  the  time  so  that  you  can 


100  MANUAL  OF  AVIATION  PRACTICE 

compute  the  actual  duration  of  your  flight  in  your 
report,  then  make  a  good  landing.  Taxy  the 
machine  to  the  spot  where  you  intend  to  leave  it 
over  night,  such  as  the  lee  of  a  hedge,  etc.;  or  if 
there  is  no  choice  of  position  taxy  the  machine  to 
the  approximate  location  from  which  you  will  make 
your  start  next  morning;  this  will  save  trouble  when 
you  get  ready  to  start. 

Dismount  from  your  machine,  lift  up  the  tail 
enough  to  leave  the  wings  edgewise  to  the  wind,  the 
machine,  of  course,  facing  the  wind,  and  jack  up  the 
tail  in  this  position  by  the  use  of  any  convenient 
prop.  Lash  the  control  wheel  or  joy  stick  fast  in  a 
fixed  position  so  that  the  wind  can  not  flap  the  con- 
trol surfaces  around  and  damage  them. 

Choose  a  sunken  trench  if  possible  in  which  the 
wheels  may  be  sunk;  if  the  wind  is  going  to  blow  and 
there  is  no  sunken  trench  it  will  be  wise  to  dig  one 
so  that  the  effect  of  the  wind  on  the  airplane  will  be 
lessened.  If  the  trench  is  not  necessary,  at  least 
put  chocks  under  the  wheels.  Peg  down  the  wings 
and  the  tail  to  stakes  driven  into  the  ground  using 
rope  if  you  can  get  some  or  lacking  this  in  an 
emergency  fence  wires  which  you  can  secure  by 
means  of  your  wire  cutters.  Do  not  lash  tightly 
enough  to  induce  strains  in  the  framework  of  the 
machine. 

Next,  fill  up  the  tanks  if  a  supply  of  gasoline  or 
oil  is  available.  Put  the  covers  on  the  propellers, 
engine,  cowls,  etc.,  in  order  that  rain  and  dew 
shall  do  no  damage  to  these  parts.  The  wings  and 


CROSS-COUNTRY  FLYING  101 

body  are  varnished  waterproof  and  will  not  be 
seriously  damaged  by  a  little  moisture;  to  avoid 
the  collection  of  moisture  in  the  wings  small  eyelet 
holes  are  sometimes  set  in  the  wings  at  the  trailing 
edge  to  let  out  the  water. 

Of  course,  you  will  engage  a  guard  to  watch  the 
machine  all  night;  see  that  a  rope  is  strung  around 
the  airplane  to  keep  off  the  crowd  which  may  collect. 

AERIAL  NAVIGATION 

Effect  of  Wind. — Navigating  in  an  airplane  is 
complicated  only  on  account  of  the  fact  that  there 
is  a  wind  blowing  which  may  not  be  in  the  desired 
direction.  While  on  the  sea  navigation  is  simple 
through  the  assistance  of  the  magnetic  compass 
(because  side  winds  can  not  materially  drift  the 
ship  sideways),  in  the  air  this  is  not  the  case;  for  if 
the  pilot  using  the  compass  points  the  nose  of  the 
airplane  directly  north  while  a  west  wind  is  blowing, 
this  wind  will  cause  the  machine  to  drift  in  an 
easterly  direction  so  that  in  an  hour  of  flight  the  air- 
plane will  be  off  its  course  by  an  amount  equal  to 
distance  which  the  wind  travels  in  1  hr.;  and  the 
joint  result  of  the  motion  of  the  airplane  forward 
and  the  motion  of  the  wind  sideways  will  cause  the 
machine  to  drift  in  a  northeasterly  direction  at  a 
speed  quite  different  from  its  rated  velocity,  and  in 
this  case  somewhat  larger.  Victor  Carlstrom  in  his 
Chicago-Newt  York  flight  found  while  he  was  over 
Cleveland  that  a  side  wind  was  deviating  his  course 


102  MANUAL  OF  AVIATION  PRACTICE 

17°  away  from  what  it  should  be,  and  if  he  had  not 
had  such  landmarks  as  the  shore  of  Lake  Erie  for 
guidance  he  might  easily  have  lost  considerable 
time. 

The  question  of  making  allowance  for  this  wind 
drift  is  very  important  where  there  are  no  land- 
marks, as  in  the  case  of  night  flying,  flying  over  the 
sea,  or  flying  over  the  clouds;  and  the  only  way  the 
pilot  can  make  allowances  for  these  conditions  is  to 
figure  them  out  before  he  starts  from  the  airdrome, 
and  plan  to  circumvent  them.  That  is  to  say,  the 
pilot  in  flight  has  no  means,  aside  from  visual 
observation  of  the  ground,  to  determine  whether  or 
not  the  wind  is  blowing  him  off  his  course.  He  must 
determine  the  whole  situation  before  he  starts,  and 
the  process  of  doing  so  is  as  follows. 

Graphical  Method  for  Determining  Direction  to 
Steer. — The  pilot  will  ascertain  from  the  weather 
vane  and  anemometer  of  the  airdrome  (1)  the 
velocity  and  (2)  the  direction  of  the  wind,  (3)  the 
speed  of  the  airplane  he  is  to  fly,  (4)  the  compass 
bearing  of  the  actual  course  which  he  desires  to 
follow.  With  this  data  it  is  possible  to  construct  a 
simple  diagram  and  to  determine  the  direction  to  be 
steered  and  the  actual  velocity  which  will  result  in 
the  proposed  journey.  A  draftsman's  scale,  pro- 
tractor and  dividers,  a  pencil  and  a  piece  of  paper  are 
the  necessary  equipment. 

When  the  wind  blows  at  an  angle  with  the  desired 
course  it  is  necessary  to  steer  the  airplane  in  such  a 
direction  that  its  own  forward  motion  will  neutral- 


CROSS-COUNTRY  FLYING  103 

ize  the  side  effect  of  the  drift  of  the  wind  from  mo- 
ment to  moment.  The  problem  is  to  determine  this 
direction  for  steering,  as  it  is  not  known.  We  are 
not  concerned  with  distances  in  this  problem,  for 
the  direction  is  going  to  be  the  same  whether  our 
flight  is  of  100  or  200  miles.  We  are,  however, 
vitally  concerned  with  velocities;  and  we  will  as- 
sume that  the  velocity  of  the  airplane  is  known  to  be 
75  miles  per  hour,  and  from  observation  on  a 
local  anemometer  the  velocity  of  the  wind  is  known 
to  be  20  miles  an  hour.  We  also  know,  of  course, 
the  direction  of  the  wind,  which  should  be  given  in 
terms  of  an  angle  whose  other  leg  points  directly 
north.  Now  if  the  flight  is  to  be  made  at  a  height 
of  2000  ft.,  as  is  usual  in  cross-country  flight  over 
average  country,  we  will  find  that  the  speed  of  wind 
will  increase  as  we  rise  up;  moreover,  that  its  direc- 
tion will  change.  In  the  present  case  the  wind  will 
be  88  per  cent,  higher  in  2000  ft.  than  it  is  on  the 
ground;  that  is  to  say,  the  velocity  at  the  altitude 
we  are  going  to  use  is  twenty  times  1.88,  or  about 
38  miles  per  hour.  Moreover,  as  the  height  in- 
creases the  direction  of  the  wind  changes,  shifting 
around  always  in  a  clockwise  direction  as  the  height 
increases,  in  the  present  case  shifting  around  16° 
from  its  ground  direction.  (The  change  of  velocity 
and  direction  for  various  heights  is  indicated  on  the 
subjoined  table.)  Thus  a  west  wind  becomes  at  a 
height  of  2000  ft.  a  slightly  northwest  wind,  or,  to 
be  exact,  blows  from  a  direction  which  is  74°  west 
of  north. 


104  MANUAL  OF  AVIATION  PRACTICE 

Our  treatment  of  the  problem  then  has  for  start- 
ing points:  velocity  of  wind,  38  miles  per  hour; 
direction  of  the  wind,  74°  west  of  north;  velocity  of 
airplane  75  miles  per  hour;  desired  direction  of 
flight  (which  has  been  determined  by  laying  out  on 
the  map  and  reading  the  compass  bearing  with  the 
protractor),  say  60°  east  of  north.  In  1  hr.  of 
flight  the  machine  would  travel  in  this  unknown 
direction  a  distance  of  75  miles  were  it  not  for  the 
wind,  but  for  every  hour  of  such  flying  the  wind  is 
blowing  it  38  miles  sideways ;  and  the  desired  direc- 
tion must  be  such  that  its  joint  effect,  together 
with  the  38  mile  sideways  wind,  will  leave  the 
machine  exactly  on  its  proper  course  at  the  end  of 
the  hour. 

On  the  map  or  piece  of  paper  denote  the  start- 
ing point  by  A  (see  Fig.  37).  From  A  draw  a 
line  parallel  to  the  wind  (that  is  to  say,  74°  west 
of  north),  and  let  this  line  represent,  to  any  con- 
venient scale,  the  speed  of  the  wind,  38  miles  per 
hour.  The  far  end  of  the  line  may  be  called  B,  and 
may  be  given  an  arrow  to  represent  the  direction 
of  wind.  Now  draw  on  the  map  a  line  from  A  to 
the  desired  destination  (C),  giving  it,  of  course  the 
proper  compass  bearing.  Take  the  dividers,  and 
with  B  as  a  center,  describe  an  arc  at  such  distance 
as  to  represent  75  miles  per  hour,  the  speed  of  the 
machine;  this  arc  will  intercept  the  line  AC  at  D, 
and  BD  then  gives  the  direction  to  steer,  for  it  is 
that  direction  which  will  permit  the  airplane  in  1 
hour  exactly  to  neutralize  the  sidewise  drift  of  the 


CROSS-COUNTRY  FLYING 


105 


wind.  The  distance  AD  on  this  diagram  can  be 
measured  off  and  will  give  the  actual  velocity  of 
movement  along  the  line  of  flight  in  miles  per  hour. 
Notice  that  it  is  97  miles  per  hour,  quite  different 
from  the  speed  of  the  airplane. 

Assuming  that  the  pilot  has  determined  the'proper 
angle   toward   which   the   airplane   nose   must   be 


FIG.  37. — Graphical    method    for    determining    direction  to    steer  to 
counteract  wind-drift.        t,-t 

pointed,  has  maintained  this  angle  throughout  his 
flight  by  means  of  the  compass  and  has  safely 
reached  his  objective;  for  the  return  trip  this  dia- 
gram must  be  completely  reconstructed  (unless  the 
wind  is  exactly  parallel  to  his  course).  The  pilot 


106 


MANUAL  OF  AVIATION  PRACTICE 


should  not  make  the  mistake  in  returning  to  the 
starting  point  of  steering  the  airplane  nose  in  a 
direction  exactly  opposite  to  the  outward  trip;  the 
reader  may  make  this  clear  to  himself  by  drawing 
the  return  diagram  and  comparing  it  with  the  out- 
ward-bound diagram. 

To  summarize  flying  when  a  cross  wind  is  blow- 
ing, it  will  be  said  that  the  direction  of  actual 
travel  will  not  be  the  direction  indicated  by  the  axis 
of  the  airplane;  and  that  therefore  while  in  a  pic- 
ture of  the  situation  the  airplane  appears  to  skid 
sideways  along  the  whole  course  it  must  be  borne 
in  mind  that  actually  there  is  no  skidding  whatever 
but  the  air  is  meeting  the  airplane  in  normal  man- 
ner. The  situation  is  analogous  to  that  of  a  fly 
going  from  one  side  to  the  other  of  the  cabin  of  a 
moving  ship,  where  the  actual  course  through  space 
of  the  fly  is  an  apparent  skid,  due  to  the  resultant  of 
its  own  and  the  ship's  movement. 

VARIATION  OF  VELOCITY  AND  DIRECTION  WITH  HEIGHT 
(25  miles  per  hour  wind) 


Height  in  feet.  .  .  . 

At  surface 

500 

1000 

2000 

3000 

4000 

5000 

Velocity    change 
in  per  cent  

100 

135 

172 

188 

196 

200 

200 

Clockwise  devia- 
tion in  degrees  .  . 

0 

5 

10 

16 

19 

20 

21 

Effect  of  Wind  on  Radius  of  Action. — Not  only 
is  the  direction  of  flight  altered  by  the  wind  but 


CROSS-COUNTRY  FLYING  107 

also  the  radius  of  action  from  a  standpoint  of  gaso- 
line capacity  is  altered.  In  the  above  machine  the 
gasoline  capacity  is  sufficient  for  3^  hr.  of  flight. 
How  far  can  it  go  across  country  and  return  before 
the  gasoline  is  used  up?  Always  allow  ^  hr. 
gasoline  for  climbing  and  for  margin;  this  leaves 
3  hr.,  which  at  75  miles  an  hour  is  225  miles,  or 
112  miles  out  and  112  miles  back.  Now  suppose 
that  a  flight  is  to  be  made  across  country  directly 
in  the  teeth  of  a  40-mile  wind;  the  radius  of  flight 
will  be  altered  as  indicated  by  the  following  calcu- 
lation: Speed  outward  is  obviously  75  minus  40 
or  35  miles  per  hour.  Speed  on  the  return  trip  is 
obviously  75  plus  40  or  115  miles  per  hour — 3.29 
times  as  fast — and  occupying  a  tune  which  may 
be  designated  by  the  letter  x.  The  time  on  the 
outward  trip  may  be  designated  by  3.29x,  a 
total  time  of  x  +  3.29x  which  we  know  equals  180 
min.  before  the  gas  runs  out.  Solve  the  equation 
x  -h  3.29z  =  180  and  we  find  that  x  is  equal  to  42 
min.,  that  is,  the  return  trip  requires  42  min.,  and 
the  outward  trip  requires  138  min.  The  distance 
covered  on  the  outward  trip  is  then  13%o  °f  35, 
which  equals  80.5  miles.  The  radius  is  then 
reduced  from  112  miles  to  80.5  miles. 

In  cases  where  the  wind  is  not  parallel  to  the 
line  of  flight  the  actual  velocity  of  course  can  not 
be  obtained  by  adding  up  the  airplane  and  wind 
velocities,  but  must  be  obtained  by  the  graph- 
ical method  mentioned  above;  thenceforward  the 
calculation  is  the  same. 


108  MANUAL  OF  AVIATION  PRACTICE 

Effect  of  Height. — Of  course  if  one  has  to  fly  in  the 
teeth  of  a  wind  and  can  choose  one's  own  altitude, 
it  is  desirable  to  fly  low  where  the  head  wind  has 
its  smaller  velocity,  and  when  flying  with  the  fol- 
lowing wind  to  rise  to  considerable  altitudes.  The 
proper  height  at  which  to  fly  will  be  about  1500 
to  3000  ft.,  for  cross-country  trips  over  ordinary 
country;  but  may  be  increased  when  the  wind  is 
unsteady  or  decreased  when  there  are  low-lying 
clouds.  The  steadiness  as  well  as  the  speed  of  the 
wind  increases  with  the  height.  The  character  of 
the  country  should  be  carefully  investigated  from 
the  profile  maps  before  starting;  all  hilly  parts 
should  be  marked  on  the  map  as  a  warning  against 
landing.  Contour  is  not  readily  distinguished  from 
a  height  of  2000  ft.  and  for  this  reason  points  may 
be  indicated  on  the  map  where  poor  landing  places 
make  it  desirable  to  fly  high.  The  character  of  the 
country  or  the  scarcity  of  landing  places  may  make 
it  advisable  to  fly  at  high  altitudes  for  the  follow- 
ing reasons:  (1)  in  case  of  engine  failure  a  good 
margin  of  height  is  necessary  to  provide  length  of 
glide  to  reach  distant  landing  places;  (2)  there  is 
then  plenty  of  space  for  righting  the  airplane  in 
case  of  bumps,  side  slips,  etc.;  (3)  eddies  or  local 
currents  due  to  inequalities  of  the  ground  do  not 
exist  to  great  heights;  (4)  landmarks  can  be  better 
distinguished  from  high  altitudes  because  the  vision 
is  better  (however,  one  must  never  trust  to  land- 
marks only  in  navigating  but  should  constantly 
use  a  compass  if  only  as  a  check,  and  especially  in 


CROSS-COUNTRY  FLYING  109 

passing  through  clouds).  Having  selected  in  ad- 
vance the  proper  height  to  use  during  the  trip 
climb  to  this  height  in  circles;  note  the  direction  of 
wind  drift  meanwhile  to  check  up  your  estimate. 
Pass  directly  over  the  point  of  departure  and  when 
over  it  point  the  nose  of  the  airplane  for  a  moment 
directly  toward  the  desired  objective  (which  can 
be  done  with  the  aid  of  the  magnetic  compass); 
select  some  distant  object  which  is  dead  ahead,  and 
therefore  directly  in  the  course;  then  head  the  nose 
of  the  machine  up  into  the  wind  just  enough  so  that 
the  direction  of  movement  will  be  straight  toward 
this  distant  object.  The  direction  of  the  nose  of  the 
machine  thus  set  by  a  method  distinct  from  the 
graphical  method  above  mentioned  should  exactly 
correspond,  however,  with  the  calculated  direction; 
and  thus  a  means  of  checking  is  obtained. 

Effect  of  Fog. — The  effect  of  fog  upon  navigating 
an  airplane  is  that  it  prevents  the  use  of  landmarks 
in  aiding  the  pilot;  also  that  it  upsets  the  pilot's 
sense  of  level.  These  two  effects  are,  of  course, 
independent  of  the  fact  that  proper  landing  places 
are  obscured,  with  resultant  peril  in  case  of  engine 
failure.  Therefore,  a  fog  should  be  avoided  when- 
ever possible;  when  one  comes  up,  the  airplane 
should  descend,  and  should  never  attempt  to  get 
above  it,  as  in  certain  localities  it  may  turn  out  to 
be  a  ground  fog.  If  the  fog  is  very  bad,  land  at  the 
earliest  opportunity.  It  is  on  account  of  fog  that 
the  pilot  avoids  river  valleys  where  frequently  there 
is  a  haze  from  the  ground  up  to  a  height  of  700  ft., 


110  MANUAL  OF  AVIATION  PRACTICE 

preventing  the  view  of  proper  landing  places  in  case 
of  necessity. 

Effect  of  Clouds  on  Navigation. — Flying  in  or 
above  the  clouds  is  a  similar  case,  inasmuch  as 
landmarks  can  not  be  seen.  It  is  not  wise  to  go 
above  the  clouds  when  on  the  sea  coast,  as  offshore 
winds  may,  unknown  to  the  pilot,  carry  him  out 
to  sea;  and  any  flight  over  the  sea  which  is  to  a 
distance  greater  than  the  safe  return  gliding  distance 
is,  of  course,  perilous. 

Navigation  by  Means  of  the  Drift  Indicator. — The 
drift  indicator  is  an  instrument  for  determining 
directly  the  side  drift  of  an  airplane.  It  enables 
the  pilot  by  looking  through  a  telescope  at  the 
ground  to  determine  exactly  what  his  direction  of 
motion  is  with  relation  to  the  ground.  The  tele- 
scope is  mounted  vertically  and  is  rotatable  about 
its  own  axis;  it  has  a  cross-hair  which  appears  in  the 
field  of  view  during  the  pilot's  observation  of  the 
ground.  As  the  airplane  speeds  overhead  objects 
on  the  ground  will  appear  through  the  telescope  to 
slip  backward  in  the  given  direction;  and  when  ac- 
customed to  the  use  of  this  instrument  the  pilot 
can  rotate  the  telescope  until  the  cross-hair  is 
exactly  parallel  to  the  apparent  line  of  motion  of 
objects  on  the  ground.  The  telescope  cross-hair 
is  parallel  to  the  axis  of  the  airplane  normally  and 
the  scale  attached  to  the  telescope  will  in  this  case 
read  zero.  When  the  pilot  rotates  the  telescope  so 
that  the  cross-hair  becomes  parallel  to  the  relative 
backward  motion  of  the  ground  the  scale  will  read 


CROSS-CO UNTR Y  FL YING  1 1 1 

something  different  from  zero  and  will  give  the  angle 
between  the  actual  line  of  motion  and  the  axis  of  the 
airplane. 

Such  a  drift  indicator  is,  of  course,  useful  only  when 
the  ground  is  visible.  The  pilot  knowing  the  angle 
between  the  airplane  axis  and  the  line  of  motion 
and  therefore  knowing  the  deviation  between  the 
supposed  course  and  the  actual  course  is  able  to 
make  corrections  and  steer  the  machine  in  its  proper 
direction.  This  may  be  done  by  altering  the 
"  lubber-line "  or  his  compass  just  enough  to  offset 
the  side  drift  of  the  machine ;  after  which  the  desired 
course  may  be  followed  by  simply  keeping  to  the 
proper  compass  bearing.  An  instrument  has  been 
devised  wherein  the  rotation  of  the  drift-indicator 
telescope  simultaneously  alters  the  lubber-line  zero. 
The  operator  then  has  merely  to  take  an  occasional 
observation  of  the  apparent  drift  line  of  the  ground, 
which  observation  automatically  shifts  the  lubber- 
line  and  navigation  proceeds  as  if  there  were  no  side 
wind  blowing  whatever.  Knowing  the  angle  be- 
tween the  direction  of  movement  and  the  airplane 
axis,  the  pilot  may  then  compute  the  speed  of  mo- 
tion in  a  manner  analogous  to  the  graphical  method 
previously  mentioned;  or  he  can  make  use  of  a  chart 
for  the  determination  of  this  speed. 

Navigation  over  Water. — In  flying  over  water  the 
presence  of  waves  is  a  valuable  guide  to  the  aviator, 
for  he  knows  that  these  waves  extend  in  a  direction 
normal  to  the  wind.  Moreover,  he  knows  that  the 
velocity  of  the  waves  bears  some  relation  to  the 


112  MANUAL  OF  AVIATION  PRACTICE 

velocity  of  the  wind.  In  order  to  estimate  the  ve- 
locity of  the  waves  it  is  only  necessary  to  know  their 
wave  length,  that  is,  the  distance  between  two  con- 
secutive wave  crests.  The  rule  is  that  for  a  wave 
length  of  10  ft.  the  velocity  is  10  miles  per  hour,  and 
will  vary  as  the  square  root  of  this  wave  length; 
that  is,  if  the  wave  length  is  half,  the  velocity  will 
be  10  divided  by  the  square  root  of  2,  or  7.1  miles 
per  hour. 


CHAPTER  VI 
THE  RIGGING  OF  AIRPLANES 

Object. — The  object  of  this  chapter  is  to  teach 
the  elementary  principles  of  correct  rigging.  It  is 
not  expected  that  the  student  will  become  an  expert 
mechanic,  but  with  this  treatment  as  a  basis  and 
through  practice  he  will  be  able  to  judge  whether 
or  not  a  machine  is  correctly  and  safely  rigged. 
In  other  words,  he  will  not  have  to  depend  on  some- 
one else's  judgment  as  to  whether  panels,  wires, 
controls,  struts,  etc.,  of  a  machine  are  in  good  order, 
but  he  will  be  able  to  observe  understandingly  that 
they  are.  If  the  engine  goes  wrong  he  can  land,  if 
the  rigging  goes  wrong  he  is  in  great  difficulty. 
Moreover,  if  the  rigging  is  wrong,  speed  is  lessened 
and  the  stability  is  uncertain. 

The  first  thing  to  be  learned  in  rigging  is  a  knowl- 
edge of  the  peculiar  terms  which  have  come  into 
use  in  aeronautics  defining  different  parts  of  the 
machines.  Our  present  list  of  terms  is  derived, 
partly  from  French,  partly  from  English,  and 
partly  from  American  terms.  Thus  different  names 
may  refer  to  the  same  part. 

NOMENCLATURE 

1.  Tractor. — An  airplane  that  is  pulled  through  the  air  by  a 
propeller  situated  in  front  of  the  machine,  is  called  a  tractor. 
113 


1 14  'MAN  UAL  OF  A  VIA  TION  PRACTICE 

2.  Pusher. — If  the  propeller  is  back  of  the  main  lifting  planes 
the  machine  is  called  a  pusher. 

3.  Fuselage  or  Body. — The  main  body  of  the  airplane  in 
which  the  pilot  sits  and  to  which  the  landing  gear,  motor, 
controls,  and  sustaining  surfaces  are  fixed.     A  small  body, 
especially  in  pusher  types  of  machines,  is  called  a  Nacelle. 

4.  Cockpit. — The  openings  and  space  in  the  fuselage  where 
pilot  or  observer  sits. 

5.  Streamline  Body. — The  shape  of  a  body  or  part  which 
permits  a  regular  flow  of  air  around  and  along  it  with  the  least 
resistance,  in  other  words  with  minimum  obstruction  and 
eddying. 

6.  Fairing. — Building  up  a  member  or  part  of  the  plane  with 
a  false  piece  that  it  may  have  a  stream-line  body. 

7.  Wings,  Planes,  Panels. — The  main  supporting  surfaces 
of  an  airplane  are  called  wings,  although  the  terms  planes  and 
panels  are  probably  as  frequently  used  and  even  preferred  by 
many.     The  term  panel  refers  properly  to  a  section  of  the 
wings  with  the  included  struts  and  wires.    The  small  panel 
directly  above  the  body  is  called  the  engine  section  panel  or 
the  center  panel,  while  the  panels  to  the  right  and  left  of 
the  body  or  fuselage  are  called  the  main  panels.     The  main 
panels  are  the  right  and  left  panels  as  seen  from  the  seat. 
Each  main  panel  may  be  subdivided  into  the  inner  wing  bay, 
the  outer  wing  bay,  and  the  overhang. 

8.  Landing  Gear,  Chassis  or  Undercarriage. — The  wheels 
and  the  struts  and  wires  by  which  they  are  attached  to  the 
fuselage. 

9.  Horizontal  Stabilizer  or  Horizontal  Fin. — The  horizontal 
fixed  tail  plane. 

10.  Vertical  Stabilizer  or  Vertical  Fin. — The  small  vertical 
fixed  plane  in  front  of  the  rudder. 

11.  Rudder.— The  hinged  surface  used  to  control  the  direc- 
tion of  the  aircraft  in  the  horizontal  plane.    As  with  a  boat, 
for  steering  or  "yawing"  or  changing  its  direction  of  travel. 

12.  Elevator  or  Flap;  Flippers.— A  hinged  horizontal  sur- 
face for  controlling  the  airplane  up  and  down,  usually  attached 


THE  RIGGING  OF  AIRPLANES  115 

to  the  fixed  tail  plane;  for  pitching  the  machine  or  "nosing  up" 
and  "nosing  down." 

13.  Tail  or   "Empennages." — A  general  name  sometimes 
applied  to  the  tail  surfaces  of  a  machine. 

14.  Mast  or  Cabane. — The  small  vertical  strut  on  top  of  the 
upper  plane  used  for  bracing  the  overhang. 

15.  Ailerons. — Movable    auxiliary    surfaces    used    for    the 
control  of  rolling  or  banking  motion.     Other  definitions  are 
that  they  are  for  the  lateral  control  or  for  maintaining  equi- 
librium.    When  they  are  a  part  of  the  upper  plane  they  are 
sometimes  called  wing  flaps. 

16.  Landing  Wires  or  Ground  Wires  (Single). — The  single 
wires  which  support  the  weight  of  the  panels  when  landing  or 
on  the  ground. 

17.  Flying  Wires,   or  Load  Wires   (Double). — The  wires 
which  support  the  body  or  fuselage  from  the  planes  when  in 
flight. 

18.  Drift  Wires. — The  horizontal  wires  which  lead  from  the 
nose  of  the  fuselage  to  the  wings  and  thus  keep  them  from  col- 
lapsing backward.     For  the  same  reason  the  wings  have  interior 
drift  wires. 

19.  Diagonal  Wires. — Any  inclined  bracing  wires. 

20.  Skids. — (a)  Tail  Skid. — The  flexible  support  under  the 
tail  of  the  machine. 

(b)  Wing  Skid. — The  protection  under  the  outer  edge  of  the 
lower  wing. 

(c)  Chassis  Skids. — Skids  sometimes  placed  in  front  of  the 
landing  gear. 

21.  Horns,  or  Control  Braces. — The  steel  struts  on  the  con- 
trols to  which  the  control  wires  are  attached. 

22.  Struts ;  Wing  Struts. — The  vertical  members  of  the  wing 
trusses  of  a  biplane,  used  to  take  pressure  or  compression, 
whereas  the  wires  of  the  trusses  are  used  to  take  pull  or  tension. 
There  are  also  fuselage  struts  and  chassis  struts. 

23.  Spar  or  Wing  Bars. — The  longitudinal  members  of  the 
interior  wing  framework. 


116  MANUAL  OF  AVIATION  PRACTICE 

24.  Rib  (Wing). — The  members  of  the  interior  wing  frame- 
work transverse  to  the  spars. 

25.  The  Longerons  or  Longitudinals. — The  fore  and  aft  or 
lengthwise  members  of  the  framing  of  the  fuselage,  usually 
continuous  across  a  number  of  points  of  support. 

26.  Engine  (Right  and  Left  Hand). — In  the  ordinary  tractor 
machine,  when  viewed  from  the  pilot's  seat  a  right-handed 
engine  revolves  clockwise  and  right-handed. 

27.  Propeller. — 

28.  Pitch    (Propeller).— The    distance    forward    that    the 
propeller  would  travel  in  one  revolution,  if  there  were  no  slip, 
that  is,  if  it  were  moving  in  a  thread  cut  at  the  same  inclina- 
tion as  the  blade.    Pitch  angle  refers  to  the  angle  of  inclination 
of  the  propeller  blade. 

29.  Slip. — Slip  is  the  difference  between  the  actual  travel 
forward  of  a  screw  propeller  in  one  revolution  and  its  pitch. 

30.  Dope. — A  general  term  applied  to  the  material  used  in 
treating  the   cloth   surface  of  airplane  members  to  increase 
strength,  produce  tautness,  and  act  as  a  filler  to  maintain  air 
and  moisture  tightness.     Usually  of  the  cellulose  type. 

31.  Controls. — Since  there  are  three  axes  or  main  direc- 
tions about  which  an  airplane  may  turn  or  rotate  it  follows 
that  three  controlling  devices  are  required.     These  are:  (1)  the 
elevator  for  pitching;  (2)  the  rudder  for  steering  or  yawing; 
(3)  the  ailerons  for  lateral,  rolling  or  banking  control. 

The  term  controls  is  a  general  term  used  to  distinguish  the 
means  provided  for  operating  the  devices  used  to  control 
speed,  direction  of  flight  and  attitude  of  the  aircraft. 

32.  Cotter  Pins. — Must  be  on  every  nut. 

33.  Castelled  Nuts.— Admit  cotter  pins. 

34.  Turnbuckles. — Must  be  well  and  evenly  threaded  and 
locked  with  safety  wires. 

35.  Safety  Wires. — For  locking  turnbuckles  and  hinge  pins. 

36.  Shackle  and  Pin.— 

37.  Hinge  Connections. — 

38.  Leading  Edge  or  Entering  Edge. — The  front  edge  of  a 
plane. 


THE  RIGGING  OF  AIRPLANES  117 

39.  Trailing  Edge. — The  rear  edge  of  a  plane. 

40.  Stagger. — The   horizontal   distance   that   the   entering 
edge  of  the  upper  wing  of  a  biplane  is  ahead  of  the  entering 
edge  of  the  lower  wing. 

41.  Dihedral  Angle. — A  term  used  to  denote  that  the  wings 
are  arranged  to  incline  slightly  upward  from  the  body  toward 
their  tips.     The  angle  made  with  the  horizontal  by  this  in- 
clination of  the  wing  is  called  the  dihedral  angle. 

42.  Angle  of  Incidence. — The  angle  at  which  a  wing  is  in- 
clined to  the  line  of  flight. 

43.  Decalage. — difference  in   angle   of  incidence   between 
any  two  distinct  aerofoils  on  an  airplane. 

44.  Chord.- — Distance  between  the  entering  edge  and  trail- 
ing edge  of  a  wing  measured  on  a  straight  line  touching  front 
and  rear  bottom  points  of  a  wing. 

45.  Camber. — The  depth  of  the  curve  given  to  a  sustaining 
surface  such  as  a  wing.     Thus  it  will  be  observed  that  the 
planes  are  not  straight  in  cross-section  but  are  concave  slightly 
upward.     The  depth  of  this  concavity  is  the  camber.     Another 
way  of  expressing  this  is  that  camber  is  the  greatest  distance 
between  the  surface  of  a  wing  and  its  chord  line. 

46.  Gap. — The  distance  between  the  lower  and  upper  wings 
of  a  biplane. 

47.  Spread. — The  distance  over  all  from  one  wing  tip  to  the 
other  wing  tip. 

48.  Aerofoil. — A  general  name  applied  to  any  wing  or  lift- 
ing surface  of  an  airplane. 

49.  Deadhead    Resistance. — Each    part    of    an    airplane 
against  which  the  wind  strikes  offers  a  resistance  against  being 
moved  through  the  air.     This  is  called  the  deadhead  resistance 
or  the  parasite  resistance.     It  is  for  the  purpose  of  lessening 
this  resistance  that  the  parts  of  a  machine  are  stream-lined. 
Remember  that  force  or  power  must  be  applied  to  overcome 
this  resistance  and  the  lessening  of  such  resistance  decreases 
the  power  necessary.    A  parallel  illustration  is  to  think  of  the 
power  necessary  to  push  a  board  sideways  through  water. 

50.  Drift. — When  the  air  strikes  the  inclined  wing  of  an 


118  MANUAL  OF  AVIATION  PRACTICE 

airplane  its  force  has  two  components.  One  part  called  the 
lift  (see  52)  acts  up  and  tends  to  lift  the  machine.  The  other 
part,  called  drift,  tends  to  push  the  machine  backward.  This 
drift  must  also  be  overcome  by  applying  power  enough  to 
drive  the  machine  forward. 

51.  Total  Resistance. — Sometimes  called  drag.     (49)  Dead- 
head resistance  added  to  (50)  drift,  gives  the  total  forces  oppos- 
ing the  forward  movement  of  the  airplane.     This  is  called  the 
total  resistance  and  is  overcome  by  the  thrust  of  the  propeller. 

52.  Lift. — (See  50).     The  upward  or  vertical  part  of  the  air 
pressure  acting  against  the  wings,  and  which  is  utilized  to  lift 
or  support  the  airplane. 

53.  Center  of  Gravity. — The  point  of  balance  of  an  airplane 
which  may  be  otherwise  defined  as  the  point  through  which  the 
mass  of  an  airplane  acts.    If  the  weight  is  too  far  forward  the 
machine  is  nose-heavy.    If  the  weight  is  too  far  behind  the 
center  of  lift  the  machine  is  tail-heavy. 

54.  Aspect  Ratio. — The  ratio  of  span  to  chord  of  a  wing  or 
any  other  aerofoil. 

55.  Gliding  Angle  (Volplane). — The  angle  made  to  the  hori- 
zontal by  the  flight  path  of  an  airplane  with  the  engine  shut 
off;  e.g.,  an  airplane  is  1000  ft.  high,  when  its  engine  fails. 
Suppose  its  gliding  angle  is  1  in  6.     Therefore,  in  still  air  it 
can  glide  6000  ft.  forward.     The  general  term  glide  refers  to 
flying  without  power. 

56.  The  Angle  of  Best  Climb. — The  steepest  angle  at  which 
an  airplane  can  climb. 

57.  Stability. — The  property  of  an  airplane  to  maintain  its 
direction  and  to  return  easily  to  its  equilibrium  or  balance  with 
a  minimum  of  oscillation.     This  is  sometimes  called  dynamical 
stability.     An  airplane  may  have   (first)   inherent  stability, 
which  is  the  stability  due  to  the  arrangement  and  disposition 
of  its  fixed  parts.     It  may  also  have  stability  with  regard  to 
any  one  of  the  three  directions  in  which  it  may  move.     These 
are  named  as  follows:  (1)  directional  stability,  with  reference 
to  the  vertical  axis;  (2)  lateral  stability  with  reference  to  the 


THE  RIGGING  OF  AIRPLANES  119 

longitudinal  (or  fore  and  aft)  axis;  (3)  longitudinal  stability, 
stability  with  reference  to  the  lateral  (or  thwartship)  axis. 

58.  Flying  Position. — Refers  to  the  position  of  the  fuselage 
when  flying.     With  the  Curtiss  J  N  4  machines  in  this  position 
the  top  longerons  are  horizontal  and  level  both  ways.     The 
engine  bearers  are  also  level,  and  the  wings  have  an  angle  of 
incidence  of  2°. 

59.  Capacity. — The  weight  an  airplane  will  carry  in  excess 
of  the  dead  load  (dead  load  includes  structure  power  plant  and 
essential  accessories) . 

60.  Flight  Path. — The  path  of  the  center  of  gravity  of  an 
aircraft  with  reference  to  the  air. 

61.  Stalling. — A  term  describing  the  condition  of  an  air- 
plane which  from  any  cause  has  lost  the  relative  speed  necessary 
for  support  and  controlling,  and  referring  particularly  to  angles 
of  incidence  greater  than  the  critical  angle. 

62.  Sweepback. — The  horizontal  angle   (if  any)   that  the 
leading  edge  of  a  machine  makes  with  the  crosswise  or  lateral 
axis  of  an  airplane. 

63.  Nose  Dive  or  Vol-pique. — A  dangerously  steep  descent, 
head  on. 


CHAPTER  VII 
MATERIALS  OF  CONSTRUCTION 

The  materials  of  construction  for  airplanes  should 
be  of  such  material,  size  and  form  as  to  combine 
greatest  strength  and  least  weight.  With  metal 
parts  in  particular  it  may  be  necessary  to  substitute 
less  strong  material  for  the  sake  of  getting  non-cor- 
rosive qualities,  ability  to  withstand  bending,  duc- 
tility or  ease  of  bending,  etc.  With  wood,  absence 
of  warping  is  important  as  well.  The  materials 
which  are  considered  are  the  following:  wood,  steel, 
including  wires;  special  metals  as  aluminum,  brass, 
monel  metal,  copper,  etc.,  and  also  linen  and  dope. 

Strength  of  Materials. — It  is  important  in  a  gen- 
eral way  to  understand  the  terms  used  in  speaking 
of  strength  of  materials.  Thus  we  may  have 
strength  in  tension,  strength  in  compression,  or 
strength  in  shearing,  bending  and  torsion.  Some 
material  fitted  to  take  tension  will  not  take  compres- 
sion, as  for  example  wire;  some  material,  as  bolts, 
are  suited  to  take  shear,  etc. 

In  general  all  material  for  airplanes  has  been  care- 
fully tested  and  no  excess  material  is  used  above  that 
necessary  to  give  the  machine  the  necessary 
strength. 

120 


MATERIALS  OF  CONSTRUCTION  121 

Tension.— This  means  the  strength  of  a  material 
which  enables  it  to  withstand  a  pull.  Thus  wires 
are  used  where  strength  of  this  kind  is  required. 

Compression. — This  refers  to  strength  against  a 
pressure.  Wire  has  no  strength  for  this  purpose, 
and  wood  or  sometimes  steel  is  used. 

Shearing. — Refers  to  strength  against  cutting  off 
sideways.  Thus  the  pull  on  an  eyebolt  tends  to 
shear  the  eyebolt,  or  the  side  pull  on  any  bolt  or  pin 
tends  to  shear  the  pin. 

Bending. — In  bending  material  the  fibres  on  the 
outside  tend  to  pull  apart ;  those  on  the  inside  tend 
to  go  together.  Thus  on  the  outside  we  have  ten- 
sion, and  on  the  inside  compression.  Along  the 
center  line  there  is  neither  tension  or  compression, 
it  is  the  "  neutral  axis." 

Torsion. — Torsion  is  a  twisting  force,  such  as  an 
engine  propeller  shaft  receives. 

Testing  for  Strength. — If  a  wire  is  an  inch  square 
in  cross-section  and  breaks  when  a  load  of  150,000 
Ib.  is  hung  on  it,  we  say  that  the  strength  of  the 
wire  is  150,000  per  square  inch.  Smaller  wires 
equally  strong  have  a  strength  of  150,000  Ib.  per 
square  inch  also,  but  they  in  themselves  will  not 
support  a  load  of  150,000  Ib.  but  only  the  fraction 
of  that,  according  to  the  fraction  of  a  square  inch 
represented  by  their  cross-section. 

In  the  same  way,  a  square  inch  of  wood  under  a 
compressive  load  may  break  at  5000  Ib.  If,  how- 
ever, the  piece  of  wood  is  long  in  proportion  to  its 
thickness,  it  will  bend  easily  and  support  much  less 


122  MANUAL  OF  AVIATION  PRACTICE 

weight.  For  example,  a  perfectly  straight  walking 
cane  could  perhaps  have  a  ton  weight  put  on  it 
without  breaking  but  if  the  cane  were  not  set 
squarely  or  if  it  started  to  bend  it  would  immediately 
break  under  the  load. 

These  cases  illustrate  the  importance  of  having 
struts  perfectly  straight,  not  too  spindling  and 
evenly  bedded  in  their  sockets.  Some  training 
machines  are  built  with  a  factor  of  safety  of  12. 
That  is  to  say,  the  breaking  strength  of  any  part  is 
twelve  times  the  ordinary  load  or  stress  under  which 
the  piece  is  placed.  It  should  be  remembered, 
however,  that  under  any  unusual  condition  in  the 
air,  such  as  banking,  etc.,  extra  strains  are  placed  on 
the  parts  and  the  factor  of  safety  is  much  less  than 
12.  Factor  of  safety  of  12  thus  does  not  mean 
exactly  what  it  does  in  other  engineering  work, 
where  allowances  are  made  for  severe  conditions. 
The  so-called  factor  of  safety  of  12  in  airplane  work 
is  probably  no  greater  than  a  factor  of  safety  of  2  or 
3  in  regular  engineering  work. 

There  are  three  all-important  features  in  the  fly- 
ing machine  construction,  viz.,  lightness,  strength 
and  extreme  rigidity.  Spruce  is  the  wood  generally 
used  for  parts  when  lightness  is  desired  more  than 
strength,  oak,  ash,  hickory  and  maple  are  all 
stronger,  but  they  are  also  considerably  heavier, 
and  where  the  saving  of  weight  is  essential,  the 
difference  is  largely  in  favor  of  the  spruce.  This 
will  be  seen  in  the  following  condensed  table  of  U. 
S.  Government  Specifications. 


MATERIALS  OF  CONSTRUCTION 


123 


Weight  per 

Modulus  of 

Compression 

WTood 

cubic  foot,      i 
pounds  (15%  ' 

rupture, 
pounds  per 

strength, 
pounds  per 

moisture) 

square  inch 

square  inch 

Hickory 

50 

16,300 

7300 

White  Oak 

46 

12,000 

5,900 

Ash  

....          40 

12,700 

6,000 

Walnut  

....          38 

11,900 

6,100 

Spruce  

....          27 

7,900 

4,300 

White  Pine  

29 

7,600 

4,800 

A  frequently  asked  question  is:  "Why  is  not  alu- 
minum or  some  similar  metal,  substituted  for  wood?" 
Wood,  particularly  spruce,  is  preferred  because, 
weight  considered,  it  is  much  stronger  than  alu- 
minum, and  this  is  the  lightest  of  all  metals.  In 
this  connection  the  following  table  will  be  of  interest. 


-Material 

Weight  in 
cubic  feet, 
pounds 

Tensile 
strength  per 
sq.in 
pounds 

Compression 
strength  per  sq.  in 
pounds 

Spruce  

27 

7,900 

4,300 

Aluminum  

162 

15,000 

12,000 

Brass  (sheet)  

510 

20,000 

12,000 

Steel  (tool)  

490 

100,000 

60,000 

Nickel  steel  

480 

100,000* 

Copper  (sheet)  

548 

30,000 

40,000 

Tobin  bronze 

(Turnbuckles)  

80,000 

Monel  metal  

540     • 

90,000 

30,000 

Wood. — Present  practice  in  airplane  construction 
is  to  use  wood  for  practically  all  framing,  in  other 
words,  for  all  parts  which  take  pressure  or  com- 

*  But  has  very  high  elastic  limit. 


124  MANUAL  OF  AVIATION  PRACTICE 

pression.  Although  wood  is  not  as  strong  for  its 
size  as  steel  and  therefore  offers  more  air  resistance 
for  the  same  strength  yet  the  fact  that  frame  parts 
must  not  be  too  spindling,  in  other  words,  that  they 
must  have  a  certain  thickness  in  proportion  to  their 
unsupported  length,  has  led  to  the  use  of  wood  in 
spite  of  the  greater  strength  of  steel.  Some  air- 
planes, however,  as  the  Sturtevant,  are  constructed 
with  practically  a  steel  framing. 

It  should  be  borne  in  mind  that  any  piece  or  kind 
of  wood  will  not  answer  for  framing,  and  more  espe- 
cially for  repair  parts.  There  is  a  tremendous  dif- 
ference in  the  strength  and  suitability  among  dif- 
ferent woods  for  the  work.  For  instance,  a  piece 
of  wood  of  cross  or  irregular  grain,  one  with  knots, 
or  even  one  which  has  been  bored  or  cut  or  bruised 
on  the  outside,  may  have  only  half  or  less  the 
strength  of  the  original  piece.  Air  drying  doubles 
the  strength  of  green  wood,  proper  oven  drying  is 
better  yet. 

Notice  how  the  ends  of  each  piece  are  ferruled, 
usually  with  copper  or  tin.  This  is  to  prevent  the 
bolt  pulling  out  with  the  grain  of  the  wood,  and  also 
prevents  splitting  and  end  checking  and  gives  a 
uniform  base  on  which  the  pressure  comes. 

It  is  generally  advised  not  to  paint  wood  as  it 
tends  to  conceal  defects  from  inspection.  So 
varnish  only. 

Wrapping  wooden  members  with  linen  or  cord 
tightly  and  doping  this,  both  to  make  waterproof 
and  to  still  further  tighten,  increases  the  resistance 


MATERIALS  OF  CONSTRUCTION  125 

to  splitting.  The  absence  of  warping  tendencies 
determine  often  what  wood  to  choose. 

The  selection  of  lumber  and  detection  of  flaws 
is  a  matter  of  experience  and  should  be  cultivated. 
It  is,  however,  nothing  more  than  the  extension 
of  the  knowledge  that  leads  a  man  to  pick  out  a 
good  baseball  bat. 

Woods. — 1.  Spruce. — Should  be  clear,  straight- 
grained,  smooth  and  free  from  knot  holes  and  sap 
pockets,  and  carefully  kiln-dried  or  seasoned.  It 
is  about  the  lightest  and  for  its  weight  the  strongest 
wood  used.  It  is  ordinarily  used  as  a  material 
for  spars,  struts,  landing  gear,  etc.,  as  it  has  a 
proper  combination  of  flexibility,  lightness  and 
strength. 

2.  White  Pine. — A  very  light  wood  used  for  wing 
ribs,  and  small  struts. 

3.  Ash. — Springy,   strong  in  tension,   hard  and 
tough,   but   is   considerably  heavier   than   spruce. 
Used  for  longerons,  rudder  post,  etc. 

4.  Maple. — Used  for  small  wood  details,  as  for 
blocks  connecting  rib  pieces  across  a  spar  or  for 
spacers  in  a  built-up  rib. 

5.  Hard  Pine. — Tough  and  uniform  and  recom- 
mended for  long  pieces,  such  as  the  wooden  braces 
in  the  wings!" 

6.  Walnut,  Mahogany,  Quarter-sawed  Oak. — The 
strength,  uniformity,  hardness  and  finishing  qual- 
ities    make   these    woods    favorites    for   propeller 
construction. 

7.  Cedar  Wood. — Is  used  occasionally  for  fusel- 


126  MANUAL  OF  AVIATION  PRACTICE 

age  coverings  or  for  hull  planking  in  hydroplanes, 
as  it  is  light,  uniform  and  easily  worked.  Veneers, 
or  cross-glued  thin  layers  of  wood,  are  sometimes 
used  for  coverings. 

Laminated  or  built-up  wooden  members  have 
been  much  used  for  framing  and  for  ribs  and  spars. 
The  engine  bearers  are  always  of  wood  on  account 
of  vibration  and  are  also  laminated.  In  lamination 
the  wooden  strut  is  built  up  of  several  pieces  of 
wood  carefully  glued  together.  The  grains  of  the 
different  layers  run  in  different  directions,  conse- 
quently a  stronger  and  more  uniform  stick  often 
is  secured.  The  objection  to  laminated  pieces 
comes  from  the  weather  causing  ungluing.  Lam- 
inated pieces  should  be  wrapped  in  linen  or  paper 
and  freshened  with  paint  or  varnish  from  time  to 
time. 

Forms. — Attention  should  be  called  to  the  hol- 
lowed form  of  many  of  the  wooden  members.  In 
any  beam  or  strut,  material  at  the  center  of  the 
cross-section  is  of  far  less  value  in  taking  the  load 
than  the  material  away  from  the  center.  There- 
fore, to  secure  greatest  strength  with  least  weight, 
it  is  permissible  to  lighten  wooden  members  if  done 
understandingly. 

Steel. — There  is  a  tremendous  difference  in  the 
strength,  wearing  and  other  desirable  qualities 
among  different  steels  and  irons.  For  airplane 
work  none  but  the  best  qualities  are  allowed.  For 
this  reason  the  use  of  ordinary  iron  bolts  (as  stove 
bolts)  or  metal  fastenings  or  wire  not  standardized 


MATERIALS  OF  CONSTRUCTION  127 

and  of  known  qualities  should  not  be  permitted. 
The  airplane  is  no  stronger  than  its  weakest  fitting. 
This  does  not  mean  that  the  hardest  and  strongest 
steel  must  necessarily  be  used,  as  ease  of  working 
and  freedom  from  brittleness  may  be  just  as  im- 
portant qualities,  but  the  steel  on  all  metal  fittings 
should  be  of  high-grade  uniform  stock.  A  ductile, 
not  too  easily  bent,  mild  carbon  steel  is  usually 
recommended  for  all  steel  plate,  clips,  sockets  and 
other  metal  parts.  If  any  parts  are  required  to  be 
tempered  or  hardened  it  must  be  remembered  that 
they  become  brittle  and  can  not  afterward  be 
bent  without  annealing  or  softening.  Tool  or 
drill  steel  is  a  name  given  to  uniform  or  rather 
reliable  grades  of  steel  adapted  to  heat  treatment  as 
tempering  or  annealing.  Often  the  bolts,  clips, 
nuts,  pins,  devices  and  other  fittings  are  of  special 
heat-treated  nickel  steel  which  must  not  be  heated 
locally  for  bending  or  for  attachment.  Such 
work  seriously  weakens  the  steel.  The  steel  is 
often  copper-  or  nickel-plated  and  enamelled  to 
prevent  rusting.  Do  not  forget  that  the  proper 
material  may  be  twice  as  strong  as  other  material 
which  looks  the  same  but  which  has  not  received 
special  treatment. 

Wires. — Only  the  highest  grade  of  steel  wire, 
strand  and  cord  is  allowable.  Manufacturers, 
as  Roebling  of  Trenton,  N.  J.,  manufacture  special 
aviator  wire  and  cord,  which  is  given  the  highest 
possible  combination  of  strength  and  toughness, 
combined  with  ability  to  withstand  bending,  etc. 


128  MANUAL  OF  AVIATION  PRACTICE 

Steel  wire  ropes  for  airplane  work  are  divided  into 
three  classes  as  follows: 

1.  The  solid  wire  =  1  wire  (as  piano- wire  grade) 
and  known  as  aviation  wire. 

2.  The  strand  stay,  consisting  either  of  7  or  19 
wires  stranded  together  and  known  as   "  aviator 
strand."     Flying  and  landing  wires  on  Curtiss. 

3.  Cord  or  Rope  Stay. — Seven   strands   twisted 
together  forming  a  rope,  each  strand  being  of  7  or 
19  wires  and  known  to  trade  as  aviator  cord.     The 
wires  are  either  tinned  or  galvanized  as  protection 
against  rust,  etc.     Ordinarily  galvanizing  is  used,  but 
hard  wires  and  very  small  wires  are  injured  by  the 
heat  of  galvanizing  and  they  are  therefore  tinned. 

No.  1.  The  single  wire  is  the  strongest  for  its 
weight.  Single  wires  will  not  coil  easily  without 
kinking  and  are  easily  injured  by  a  blow,  therefore 
their  use  is  confined  to  the  protected  parts  of  the 
machine  such  as  brace  wires  in  the  fuselage  and  in 
the  wings. 

The  strand  stay  (No.  2)  of  7  or  19  wires  is  gener- 
ally used  for  tension  wires,  as  it  is  more  elastic  (can 
be  bent  around  smaller  curve)  without  injury,  as 
the  flying  and  landing  wires  on  the  Curtiss.  The 
smaller  strands  usually  have  7  wires,  the  larger 
ones  19  wires. 

No.  3.  The  Tinned  Aviator  Cord.— The  7  by  19 
cord  is  used  for  stays  on  foreign  machines.  It  is 
1%  times  as  elastic  as  a  solid  wire  of  the  same 
material.  On  the  Curtiss  it  is  used  for  control 
wires.  For  steering  gear  and  controls  extra  flexible 


MATERIALS  OF  CONSTRUCTION  129 

aviator  cord  is  also  recommended.  This  has  a 
cotton  center  which  gives  extra  flexibility  and  is 
used  for  steering  gear  and  controls.  It  is  2>^  times 
as  elastic  as  a  single  wire. 

Although  wire  strands  or  cords  are  not  quite  as 
strong  for  the  same  size  as  a  single  wire  they  are 
preferred  for  general  work,  being  easier  to  handle 
and  because  a  single  weak  spot  in  one  wire  does  not 
seriously  injure  the  whole  strand. 

Especial  care  is  necessary  to  avoid  using  common 
steel  wires,  or  strands  which  have  a  frayed  or  broken 
wire,  or  wire  that  has  been  kinked  and  then 
straightened  or  wire  that  has  been  locally  heated 
or  wire  that  has  been  bruised.  All  these  factors 
weaken  steel  rope  much  more  than  is  supposed 
ordinarily. 

Wire  Fastening  or  Terminal  Connections. — Wire 
terminals  are  of  four  classes: 

1 .  Ferrule  and  dip  in  solder,  then  bend  back  the  end. 
With  or  without  thimble;  used  on  single  wires  or  on 
strand;  50  to  94  per  cent,  as  strong  as  the  wire. 

2.  Thimble  and  End  Splicing. — The  splice  must 
be  long  and  complete.     Used  on  cable;  80  to  85  per 
cent,  as  strong  as  the  strand;  breaks  at  last  tuck  in 
the  splice. 

3.  Socket. — Nearly  100  per  cent,  strong. 

4.  End  Wrap  and  Solder. — Simple  and  serviceable ; 
not  used  for  hard  wire. 

Present  practice  is  rather  toward  elimination  of 
acid  and  solder,  imperfect  bends,  flattening  of  cable 
on  bends,  and  toward  care  in  avoiding  all  injury  as 


130  MANUAL  OF  AVIATION  PRACTICE 

kinking  to  wire,  strand  and  cord  due  to  unskillful 
handling  of  material  in  the  field. 

Other  Metals. — Other  metals  as  aluminum,  brass, 
bronze,  copper,  monel  metal  (copper  and  nickel) 
are  used  for  certain  airplane  fittings  for  the  reasons 
of  lightness,  non-corrosive  qualities,  or  ease  of 
bending,  etc.  The  trouble  with  these  metals  is 
that  they  are  not  uniform  and  reliable  in  strength 
and  in  an  important  part  the  great  strength 
combined  with  minimum  weight  given  by  steel 
is  not  equalled  by  any  of  these  metals.  Aluminum 
is  used  on  the  engine  hood  and  also  for  control  levers 
and  for  the  backs  of  the  seats.  In  other  words,  for 
parts  and  castings  which  require  light  metal  con- 
struction, but  which  are  under  no  particular  stress. 
Tin  and  copper  are  used  for  ferrules  of  wire  joints 
and  for  tankage.  Copper  or  brass  wire  are  used 
for  safety  wires.  Special  Tobin  bronze  is  used  for 
turnbuckles  as  the  part  must  not  only  be  strong  but 
free  from  any  tendency  to  rust.  Monel  metal 
(nickel  60  per  cent.,  copper  35  per  cent.,  iron  5 
per  cent.)  is  strong  and  has  the  special  property  of 
being  acid-  and  rust-resisting.  It  has  been  used 
for  metal  fittings  and  even  for  wires  and  for  the 
water  jacket  of  the  motor.  Until  more  strength 
tests  show  greater  uniformity  of  strength,  it  is 
to  be  recommended  with  caution. 

In  dealing  with  metals  like  steel,  it  should  be  re- 
membered that  they  are  subject  to  crystallization 
and  fatigue. 

Repeated  jarring  may  cause  a  bar  of  steel  to 


MATERIALS  OF  CONSTRUCTION  131 

break  easily  at  a  particular  point,  when  the  metal  is 
said  to  have  crystallized  there. 

Fatigue  of  a  metal  may  be  defined  as  loss  of 
springiness  which  may  come  from  repeated  bending 
and  which  lessens  the  strength  of  metal.  Above 
all,  however,  corrosion  of  steel  must  be  guarded 
against. 

The  above  points  should  be  clear,  as  in  airplane 
work  you  are  dealing  with  a  structure  which  is 
safe  with  perfect  materials  and  workmanship. 
The  factor  of  safety,  however,  is  not  great  enough 
to  permit  carelessness,  or  defective  material. 

Linen. — The  almost  universal  wing  covering  is 
fine,  unbleached  Irish  linen,  stretched  rather  loosely 
on  the  wing  frames  and  then  treated  with  dope. 

The  linen  used  weighs  3%  to  4%  oz.  per  square 
yard,  and  should  have  a  strength  with  the  length  of 
the  cloth  or  uwarp"  of  at  least  60  Ib.  per  inch  of 
width.  The  strength  in  this  direction  is  slightly 
greater  than  that  taken  crosswise  of  the  cloth  or  on 
the  filler  or  weft.  There  is  a  gain  of  strength  and 
tautness  by  varnishing  or  "doping." 

In  general,  it  is  desirable  to  have  wing  material 
which  will  not  sag  easily  and  have  the  fabric  yield 
rather  than  break.  This  often  reduces  stress  and 
saves  complete  failure. 

Dope. — The  linen  must  be  coated  with  a  more 
or  less  waterproof  dope.  Some  form  of  cellulose 
acetate  or  nitrate  with  more  or  less  softening  mate- 
rial is  used  and  to  these  some  suitable  solvent  as 
acetone  is  added. 


132  MANUAL  OF  AVIATION  PRACTICE 

The  cellulose  acetate  or  nitrate  in  the  dope  acts 
as  a  waterproof  sizing,  shrinks  the  cloth  tight,  and 
prevents  it  from  changing  in  tightness  due  to 
moisture.  Spar  varnish  protects  this  layer  from 
peeling  and  makes  the  wing  more  waterproof.  In 
service,  varnish  or  dope  must  be  applied  every 
few  weeks. 

The  U.  S.  Army  practice  calls  for  four  coats  of 
cellulose  nitrate  dope  followed  by  two  coats  of  spar 
varnish  to  prevent  inflammability.  Cellulose  ni- 
trate is  more  elastic  and  durable  than  the  acetate 
but  is  also  more  inflammable. 

Commercial  dopes  with  various  desirable  prop- 
erties are:  Cellon,  Novavia,  Emaillite,  Cavaro, 
Titanine,  etc. 


CHAPTER  VIII 
ERECTING  AIRPLANES 

Airplanes  shipped  from  the  manufacturer  or  from 
another  field  almost  always  suffer  more  or  less  from 
shipment  or  packing.  Care  must  be  exercised  in 
unpacking  in  order  not  to  do  any  more  damage. 
Boxes  should  be  placed  with  the  part  marked 
"Top"  uppermost.  Cables  and  wires  must  be 
handled  carefully  in  order  not  to  bend  or  twist 
them.  Every  bent  or  kinked  wire  or  damaged 
turnbuckle  must  be  replaced,  or  at  least  brought  to 
the  attention  of  an  inspector. 

The  order  of  erection  is  as  follows : 

1.  Assemble  landing  gear  to  fuselage  and  align 
landing  gear  before  putting  on  main  panels. 

2.  Assemble  tail. 

3.  Assemble  engine  section  and  align  before  at- 
taching main  panels. 

4.  Assemble  main  panels. 

1.  Landing  Gear  Assembly  to  Fuselage. — The 
landing  gear  is  assembled  by  mounting  the  wheels 
on  the  axle,  and  bolting  wheels  in  place.  The 
fuselage  should  now  be  elevated  to  receive  the  land- 
ing gear.  This  may  be  accomplished  in  one  of  two 
ways — either  by  tackle  or  by  shims  and  blocking. 
For  either  method,  first  connect  up  the  tail  skid. 

133 


134  MANUAL  OF  AVIATION  PRACTICE 

This  is  accomplished  by  pinning  up  the  front  end 
of  the  skid  to  the  spring-fitting,  and  then  pinning 
in  the  other  end  to  the  tail-post  socket. 

If  block  and  tackle  are  used  to  raise  the  fuselage, 
pass  a  line  under  the  engine-bed  supports  or  sills 
just  to  the  rear  of  the  radiator.  To  this  line  attach 
hook  of  block.  To  avoid  damaging  or  crushing 
some  part  do  not  attach  lifting  device  to  any  other 
point.  With  the  fuselage  now  resting  on  its  at- 
tached tail  skid,  lift  the  front  end  until  the  lower 
longeron  clips  clear  the  landing  gear.  When  the 
clips  on  the  longerons  line  up  with  the  clips  on  the 
ends  of  the  struts  of  the  landing  gear  the  bolts  are 
passed  down  through  the  holes  thus  aligned.  This 
places  the  nuts  on  the  down  side  of  the  connection 
thus  facilitating  assemblies  and  inspection  of  con- 
nections. The  castellated  nuts  are  then  put  on 
the  bolts  and  drawn  up  tight,  until  the  drilled  hole 
in  the  bolt  is  visible  through  the  castle  of  the  nut. 
Then  insert  cotter-pin  and  spread  the  two  leaves 
backward  over  the  nut.  This  locks  the  nut  in 
place.  When  the  landing  gear  has  been  completely 
assembled  to  the  fuselage,  the  tail  of  the  machine 
should  be  elevated  and  supported  by  a  horse  and 
blocking  until  the  upper  longeron  is  level.  This 
can  be  determined  by  placing  a  spirit  level  on  the 
upper  longeron  at  the  tail  or  on  the  two  engine-bed 
sills  in  machines  where  these  sills  are  parallel  to  the 
top  longeron,  as  in  Curtiss  JN-4B. 

2.  Horizontal  Stabilizer. — After  the  upper  long- 
eron is  levelled  up,  the  horizontal  stabilizer  is  as- 


ERECTING  AIRPLANES  135 

sembled  to  the  tail  of  the  fuselage.  The  horizontal 
stabilizer  is  fastened  by  means  of  bolts  in  the  top 
longeron  and  the  tail  post.  The  nuts  are  all  drawn 
up  tight  and  cotter-pinned.  The  vertical  stabilizer 
is  next  erected  in  place. 

3.  Vertical  Stabilizer. — The  vertical  stabilizer  is 
now  fastened  to  the  horizontal  stabilizer,  first  by 
means  of  the  bolt  which  passes  up  through  the  for- 
ward part  of  the  horizontal  stabilizer  and  then  by 
means  of  the  flexible  stay  lines  running  from  the 
top  of  the  vertical  stabilizer.     The  forward  bolt 
passes  through  the  clip  at  the  lower  front  point  of 
the  vertical  stabilizer.     Draw  the  nuts  up  tight 
and  lock  with  cotter-pins.     Flexible  wire  cables  are 
attached  to  vertical  stabilizer,  and  turnbuckles  are 
used   to   align   and   tighten   cables.     The   vertical 
stabilizer  is  further  aided  in  its  alignment  by  the 
bolt  clip  at  its  toe  and  by  the  double  clip  at  its  heel. 
This  rear  double  clip  passes  over  the  two  bolts  which 
are  attached  to  the  tail  post  and  which  hold  down 
the  horizontal  stabilizer. 

4.  Rudder. — The    control    braces    are    first    at- 
tached to  the  rudder.     These  braces  are  so  placed 
that  the  upper  tips  point  toward  the  hinge  line.     In 
this  fashion  the  holes  will  match  up.     The  rudder  is 
mounted  on  the  tail  post  and  vertical  stabilizer  by 
means  of  the  hinges.     The  hinge  pins  are  inserted 
in  the  hinges,  and  cotter-pins  passed  through  the 
drilled  holes  in  the  bottom  of  the  pins.     The  cotter- 
pins  should  be  spread  backward  as  usual. 

5.  Elevators  or  Flaps. — These  are  first  equipped 


136  MANUAL  OF  AVIATION  PRACTICE 

with  the  control  braces  which  are  also  arranged  so 
that  the  upper  tips  point  toward  the  hinge  line. 
The  elevators  are  mounted  to  the  horizontal  stabil- 
izer by  means  of  the  hinges  and  hinge  pins.  The 
hinge  pins  are  kept  in  their  bearings  by  the  cotter- 
pins,  inserted  through  the  drilled  holes  in  the  bottom 
of  the  hinge  pins. 

6.  Panel  Assembly. — The  panels  are  now  to  be 
assembled.     Before  the  main  panels  can  be  con- 
nected to  the  fuselage,  the  engine  section  panel 
must  be  erected. 

Engine  Section  Panel. — The  engine  section  struts 
are  first  set  into  place  in  their  sockets  on  the  engine 
section.  Then  the  whole  thing  is  lifted  up  to  place 
and  the  four  struts  are  set  into  their  sockets  on  the 
upper  longeron.  The  bracing  wires  are  attached 
and  the  engine  section  aligned  by  means  of  them 
(see  alignment). 

7.  Main  Panels. — The  main  panels  are  now  to  be 
assembled  to  the  machine.     There  are  two  methods 
for  accomplishing  this :  first,  assemble  panels,  struts 
and  wires,   before  attaching  to   fuselage;   second, 
assemble  the  upper  plane  to  the  engine  section,  and 
complete  assembly.     The  first  method  is  the  most 
advantageous,  since  it  permits  the  setting  of  the 
main  panels  at  the  correct  stagger  and  dihedral,  and 
does  not  require  as  much  adjustment  as  the  second 
method,  which  will  be  omitted. 

Assembling  Panels  Together  Before  Fastening 
Them  to  Fuselage. — All  the  main  struts  will  be 
found  to  bear  a  number.  These  numbers  run  from 


ERECTING  AIRPLANES  137 

1  to  8,  on  Curtiss  JN-4.  The  numbers  on  the 
Standard  run  from  1  to  12  including  the  center  sec- 
tion struts.  The  method  used  in  numbering  the 
posts  is  as  follows:  Starting  at  post  No.  1,  with  the 
outer  post,  on  the  left-hand  side  of  the  pilot,  as  he 
faces  his  direction  of  travel,  the  posts  are  numbered 
successively  from  No.  1  to  No.  4;  Nos.  1  and  2  being 
on  the  left  side  and  Nos.  3  and  4  being  on  the  right 
side.  The  rear  posts  are  similarly  numbered  from 
No.  5  to  No.  8,  Nos.  5  and  6  being  on  the  left  and 
Nos.  7  and  8  being  on  the  right.  This  system  of 
numbering  does  not  include  the  engine  sec- 
tion struts.  The  plan  shows  the  system  graphically 
(see  Fig.  39). 

The  system  of  marking  also  insures  that  the  struts 
are  not  inverted  in  their  sockets.  This  is  accom- 
plished by  painting  the  number  on  the  strut,  so 
that  when  viewed  from  the  pilot's  seat,  all  numbers 
can  be  read,  i.e.,  the  numbers  are  painted  on  that 
side  of  the  strut  intended  to  face  the  fuselage.  If 
a  strut  is  inverted  by  mistake,  it  can  thus  be  quickly 
detected.  The  procedure  of  assembling  panels  is  as 
follows : 

1.  The  upper  left-wing  panel  is  first  equipped 
with  mast,  by  inserting  the  mast  into  its  socket  on 
the  upper  surface  of  the  wing.     The  mast  wire  is 
then  connected  up  to  the  clips  to  the  right  and  left 
of  the  mast.     Adjust  the  tension  in  this  wire,  by 
means    of    turnbuckles,    until    the    spar    becomes 
straight. 

2.  Stand  the  upper  left-wing  panel  and  lowerleft- 


138  MANUAL  OF  AVIATION  PRACTICE 

wing  panel  on  their  " leading"  or  " entering" 
edges,  properly  supporting  the  panels  in  cushioned 
blocks  to  prevent  damage  to  the  nose.  Space  the 
panels  apart,  at  a  distance  approximately  equal  to 
the  length  of  the  struts. 

3.  Next   connect  up   the   diagonal   cross   wires. 
These  must  be  loosely  connected  up,  to  permit  the 
easy  entering  of  the  posts  into  the  sockets.     The 
wires  are  connected  before  the  posts  or  struts  are  set 
in  place,  since  with  the  latter  in  place,  the  connect- 
ing of  the  wires  to  the  lugs  of  the  sockets  is  accom- 
plished only  with  difficulty.     After  these  wires  are 
thus  connected,  insert  the  posts  and  bolts  into  place. 

4.  Connect   up   closely   the   "landing"    (single) 
wires,  and  " flying"  (double)  wires  of  the  outer  bay 
to  hold  the  wings  together  as  a  unit.     The  outer  bay 
is  thus  completely  wired,  though  but  loosely. 

5.  The  posts  that  are  used  for  this  left  side  are, 
according  to  the  diagram,  No.  1,  No.  2,  No.  5,  No.  6. 
No.  1  is  the  outer  front;  No.  2  is  the  inner  front; 
No.  5  is  the  outer  rear;  No.  6  the  inner  rear. 

6.  The    wings,    as    above    assembled,     are  now 
erected  to  the  fuselage.     Extreme  care  should  be 
exercised  in  transferring  the  wings  to  the  fuselage, 
not  to  strain  or  break  them.     In  carrying  the  wings, 
use  wooden  boards  placed  under  the  wings,  and 
block  up  under  the  wing  beams   (which  can  be 
easily  located),  so  that  these  take  the  strain  of  the 
load.     Do  not  attempt  handling  assembled  wings, 
using  the  posts  as  carriers;  or  by  attachments  to  the 
trailing  or  leading  edges.     The  wings  should  be 


ERECTING  AIRPLANES  139 

suitably  supported  temporarily  by  suitable  sling  at 
the  outer  upper  post  point  (not  beyond  this  point) 
or  by  a  horse,  properly  blocked  under  lower  wing  at 
outer  lower  post  point  (not  beyond  this  point) 
during  fitting  of  wing  to  machine.  The  wings  will 
have  the  approximate  stagger  if  assembled  as 
above,  since  the  posts  are  in  place,  and  the  tension 
cross  wires  are  adjusted  to  almost  correct  length 
when  shipped.  Insert  the  hinge  pins  through  the 
hinges  as  now  coupled  up,  lower  hinges  first. 

The  machine  is  now  ready  for  alignment,  perhaps 
the  most  important  of  the  rigger's  duties. 

Alignment  of  Airplanes.— The  proper  alignment 
of  a  machine  largely  determines  the  flying  qualities 
of  that  machine. 

The  alignment  of  the  fuselage  should  be  done  at 
the  factory  or  in  the  repair  shop.  However,  the 
alignment  of  the  whole  machine  depends  upon  the 
correctness  of  the  fuselage.  Directions  for  aligning 
and  checking  fuselage  are,  therefore,  given. 

The  order  in  which  the  different  parts  of  a  ma- 
chine should  be  aligned  is  as  follows : 

1.  Alignment  of  landing  gear. 

2.  Alignment  of  center  section. 

3.  Alignment  of  leading  edge. 

4.  Getting  both  wings  the  same  height. 

5.  Dihedral  angle,  if  any. 

6.  Alignment  of  trailing  edge  (angle  of  incidence). 

7.  Stagger. 

8.  Droop. 

9.  Tightening  and  safetying  all  wires. 

10.  Length  of  struts,  positions  and  fittings,  warp  in  planes. 


140  MANUAL  OF  AVIATION  PRACTICE 

11.  Alignment  of  ailerons. 

12.  Alignment  of  stabilizer. 

13.  Alignment  of  elevator  flaps. 

14.  Alignment  of  rudder. 

The  tail  of  the  machine  should  be  raised  until 
the  fuselage  is  nearly  horizontal  before  starting  the 
alignment. 

1.  Alignment  of  Landing  Gear. — When  a  machine 
is  being  assembled,  it  is  easier  to  align  the  landing 
gear  before  the  wings  are  put  on. 

Take  the  weight  off  the  landing  gear  by  supporting 
the  fuselage  on  sawhorses. 

The  axle  should  be  parallel  with  the  lateral  axis 
of  the  machine. 

The  center  of  the  axle  should  be  directly  under 
the  center  of  the  fuselage.  This  can  be  secured  by 
either  of  two  methods : 

(a)  By  Measuring  Cross  Distances. — Loosen  and 
tighten  the  cross  wires  until  the  cross  distances  are 
exactly  the  same.  Take  all  measurements  from 
similar  points  on  the  fittings  to  which  the  wires  are 
attached. 

(6)  With  Level  and  Plumb  Bob.— Level  the  fusel- 
age crosswise.  Mark  the  exact  center  of  the  fusel- 
age and  drop  a  plumb  bob.  Mark  the  exact  center 
of  the  axle.  Adjust  the  cross  wires  until  the  plumb 
bob  is  over  the  center  of  the  axle.  Tighten  the 
wires  until  fairly  tight,  and  safety  them. 

2.  Alignment  of  the  Center  Section. — When  as- 
sembling a  machine,  the  center  section  should  be 
aligned  before  the  wings  are  put  on. 


ERECTING  AIRPLANES 


141 


When  a  machine  is  already  assembled,  the  first 
thing  to  do  is  to  loosen  all  wires  except  the  landing 
wires.  This  is  very  important,  for  if  one  wire  is 
tightened  against  another  wire,  an  unnecessary  and 
possibly  a  dangerous  strain  may  be  put  upon  some 
member.  The  bracing  wires  connecting  tops  of 
center  section  struts  should  be  tight  enough  to  hold 
the  shape  of  the  center  section  when  bracing  wires 
are  tightened  up. 


r  by  means  of 
Hinges 
(b) 

FIG.  38. — Center  section  and  undercarriage  alignment. 

(a)  Machines  Having  No  Stagger. — In  machines 
having  no  stagger,  the  struts  of  the  center  section 
should  be  perpendicular  to  the  propeller  axis.  As 
the  upper  longerons  are  usually  parallel  to  the  pro- 
peller axis,  they  may  be  used  as  a  base  line. 

Align  one  side  of  the  center  section  first,  then  the 
other  side,  and  lastly  the  front. 

From  a  point  at  the  lower  end  of  one  of  the  front 


142  MANUAL  OF  AVIATION  PRACTICE 

center  section  struts  (the  center  of  a  bolt  head  for 
example),  measure  forward  on  the  longeron  a  certain 
distance.  From  the  same  point  (center  of  bolt  head) 
measure  back  on  the  longeron  exactly  the  same 
distance. 

Move  the  upper  end  of  the  strut  forward  or  back- 
ward by  loosening  one  of  the  bracing  wires  and 
tightening  the  other,  until  the  distance  from  the 
two  points  on  the  longerons  to  some  point  on  the 
center  line  at  the  top  of  the  strut  (center  of  bolt 
head)  are  exactly  the  same.  The  strut  will  then 
be  perpendicular  to  the  propeller  axis.  Tighten 
both  wires  evenly  until  fairly  tight.  Measure  the 
cross  distances  (the  diagonal  distances  between 
similar  points  at  the  upper  and  lower  ends  of  the 
front  and  rear  struts),  and  align  the  other  side  of 
the  center  section  until  its  cross  distances  are  the 
same  as  those  on  the  opposite  side. 

Align  the  front  of  the  center  section  by  loosening 
one  cross  wire  and  tightening  the  other,  until  one 
cross  distance  is  exactly  the  same  as  the  other  cross 
distance. 

(6)  Machines  Having  Stagger. — In  machines 
having  stagger,  the  shape  and  position  of  the 
center  section  strut  fittings  usually  determines  the 
amount  of  stagger  the  machine  was  designed  to  have 
(Fig.  38-a).  The  JN-4  has  10%-in.  stagger,  i.e., 
a  plumb  line  dropped  from  the  leading  edge  of 
upper  panel  should  be  10%-in.  from  leading  edge 
of  lower  panel. 

Adjust  the  wires  on  one  side  of  the  center  section 


ERECTING  AIRPLANES  143 

until  the  struts  and  that  side  are  in  their  correct 
positions  as  shown  by  the  shape  of  the  fittings. 
Tighten  the  wires,  measure  the  cross  distances,  and 
adjust  the  wires  on  the  other  side  of  the  center  sec- 
tion until  the  cross  distances  are  exactly  similar 
to  the  first  set. 

A  more  accurate  method  is  to  drop  a  plumb  line 
from  the  leading  edge  of  the  center  section  and  ad- 
just until  the  line  is  at  the  correct  distance  ahead 
of  the  point  on  the  fuselage  where  the  leading  edge 
of  the  lower  wing  meets  it.  This  point  may  be  de- 
termined by  measuring  the  distance  from  the  inside 
of  the  front  hinge  to  the  leading  edge  of  the  lower 
wing  and  then  laying  off  this  distance  on  the  body 
from  the  front  of  the  hinge  on  the  lower  longeron. 
Better  still,  if  the  hinges  are  at  the  same  distance 
from  the  leading  edge  on  both  top  and  bottom  wings, 
the  plumb  line  may  be  dropped  from  the  front  side 
of  the  hinge  on  the  center  section  and  the  stagger 
measured  back  to  the  hinge  on  the  lower  longeron 
(Fig.  38-6).  This  has  the  advantage  of  setting  the 
plumb  line  out  far  enough  to  clear  the  fuselage. 
Also  the  measurements  are  easily  made. 

Next,  adjust  the  two  front  wires  until  one  cross 
distance  is  exactly  the  same  as  the  other  cross  dis- 
tance (Fig.  38-c). 

3.  Alignment  of  Leading  Edge. — (a)  Upper 
Plane. — The  leading  edges  of  the  upper  and  lower 
planes  of  one  wing  should  next  be  made  perfectly 
straight.  By  standing  on  a  step  ladder,  placed  15 
to  20  ft.  to  one  side,  and  sighting  along  the  leading 


144  MANUAL  OF  AVIATION  PRACTICE 

edge  of  the  upper  plane,  any  bow  or  warp  can  be 
easily  seen.  This  should  be  straightened  out  by 
loosening  or  tightening  the  front  landing  wires. 
The  edge  should  be  brought  in  exact  line  with  the 
leading  edge  of  the  center  section. 

(6)  Lower  Plane. — After  the  leading  edge  of  the 
upper  plane  has  been  made  straight,  sight  along  the 
leading  edge  of  the  lower  plane.  If  there  is  no  warp 
in  the  plane,  this  edge  should  also  be  straight. 

(c)  Align  the  opposite  wing  in  the  same  manner. 

4.  Getting  Both  Wings  the  Same  Height.— Place 
a  small  tack  exactly  in  the  middle  of  the  leading 
edge  of  the  center  panel. 

Measure  from  this  tack  to  similar  points  at  the 
lower  ends  of  the  intermediate  and  outer  struts 
(Fig.  39).  Make  these  distances  the  same  on  each 
side  by  raising  or  lowering  one  wing  or  the  other, 
or  by  raising  one  wing  and  lowering  the  other  wing, 
all  the  while  keeping  the  leading  edges  of  both  wings 
perfectly  straight. 

5.  Dihedral. — The  method  of  setting  the  wings 
of  a  machine  at  a  dihedral  angle  is  as  follows : 

Place  two  tacks  in  the  leading  edge  of  the  upper 
plane,  one  tack  near  the  tip  of  each  wing  and  exactly 
the  same  distance  out  from  the  tack  in  the  center 
section.  Stretch  a  string  tightly  between  the  two 
outer  tacks,  until  there  is  no  sag  in  the  string. 

A  dihedral  angle  of  178°  means  that  each  wing  has 
been  raised  1°.  To  set  the  wings  of  a  machine  at  a 
dihedral  angle  of  178°  for  example: 

(a)  Find  the  natural  sine  of  1°  (0.0175). 


ERECTING  AIRPLANES 


145 


(6)  Multiply  this  by  the  distance  in  inches  be- 
tween the  center  tack  and  one  of  the  outer  tacks. 
The  result  will  give  the  rise,  in  inches,  of  the  string 
over  the  tack  in  the  center  section. 

Raise  the  wings  equally,  keeping  the  leading  edges 
perfectly  straight,  until  the  proper  rise  shows  over 
the  center  section. 


OVERALL  ADJUSTMENTS 
(SHOWS  ALSO  luffTISS  "STRUT  NUMBERING 


"STANDARD"STRUT  NUMBERING 


DIHEDRAL    ANGLE 


FIG.  39. — Alignment  diagrams. 

6.  Alignment  of  Trailing  Edge  (Angle  of  Inci- 
dence).— (a)  Lower  Plane. — The  trailing  edge  should 
be  brought  parallel  to  the  leading  edge.  This  can 
be  done  by  bringing  the  rear  spar  in  line  with  the 
leading  edge. 

Stand  squarely  in  front  of  the  center  of  the  ma- 


146  MANUAL  OF  AVIATION  PRACTICE 

chine  15  to  20  ft.  away.  Sight  under  the  leading 
edge  of  the  lower  plane;  move  forward  or  backward 
until  the  fittings  under  the  rear  spar  are  just  visible. 
Raise  or  lower  the  trailing  edge  by  loosening  or 
tightening  the  rear  landing  wires,  until  all  of  the 
fittings  on  the  rear  spar  appear  equally  under  the 
leading  edge. 

(6)  Upper  Plane. — After  aligning  the  trailing 
edge  of  the  lower  plane,  place  a  ladder  in  front  of  the 
center  of  the  machine,  and  sight  under  the  leading 
edge  of  the  upper  plane.  If  there  is  no  warp  in  this 
plane,  the  trailing  edge  should  align  with  the  lead- 
ing edge. 

The  objection  to  this  method  is  that  since  there 
are  no  fittings  next  the  body  on  the  rear  spar,  there 
is  room  for  considerable  error  in  the  angle  of  inci- 
dence. 

Reversing  the  process  and  finding  the  angle  of 
incidence  at  each  set  of  struts  secures  the  align- 
ment of  the  trailing  edge  and  removes  the  liability  to 
error.  To  set  wings  at  correct  angle  of  incidence 
proceed  as  follows  (Fig.  39) :  Place  the  airplane 
in  rigging  position,  i.e.,  level  up  the  top  longeron  or 
engine  bearers.  Set  the  corner  of  the  straight  -edge 
against  the  center  of  the  rear  spar,  level  up  the 
straight-edge,  and  measure  from  the  top  of  the 
straight-edge  to  the  center  of  the  front  spar  or  to  the 
lowest  point  of  the  leading  edge.  This  must  be 
done  next  the  body  and  under  each  set  of  struts. 
(It  is  useless  to  make  such  a  measurement  between 
the  struts  because  of  possible  warping  of  the  wings.) 


ERECTING  AIRPLANES  147 

Unless  the  wings  have  a  washout  or  washin  the 
measurements  must  agree,  thus  making  the  angle 
of  incidence  the  same  all  along  the  wing.  Then 
the  trailing  edge  must  necessarily  be  parallel  to  the 
leading  edge. 

7.  Stagger. — The  stagger  should  be  the  same  all 
along  the  wing  as  it  is  for  the  center  section.     With 
the  machine  in  rigging  position  drop  a  plumb  line 
from  the  leading  edge  of  the  upper  wing  in  front  of 
each  set  of  struts.     The  distance  from  the  plumb 
line  to  the  lower  edge  should  equal  the  stagger.     If 
there  is  too  much,  tighten  the  diagonal  wire  running 
from  the  lower  rear  socket  to  the  upper  front  socket, 
being  sure  that  the  other  diagonal  wire  is  loosened 
somewhat.     For  too  little  stagger  tighten  the  latter 
and  loosen  the  former  wire. 

Check  up  the  dihedral  and  alignment  of  the  trail- 
ing edges  to  see  if  these  have  been  disturbed  while 
setting  the  stagger.  If  not,  the  droop  may  be  put 
in. 

8.  Droop. — To  correct  for  the  torque  of  the  pro- 
peller, one  wing  of  a  machine  is  slightly  drooped. 

In  single-motored  tractor  types,  if  the  propeller 
turns  to  the  right,  when  looking  from  the  rear,  the 
left  wing  is  drooped,  and  vice  versa. 

The  outer  rear  landing  wire  of  the  wing  to  be 
drooped  should  be  loosened  until  the  trailing  edge, 
between  the  outer  and  intermediate  struts,  appears 
to  be  about  an  inch  (for  machines  of  not  more  than 
100  hp.)  lower  than  the  rest  of  the  trailing  edge. 
The  practice  with  the  Curtiss  JN-4B  is  to  loosen  the 


148  MANUAL  OF  AVIATION  PRACTICE 

inner  rear  landing  wire  on  the  left  wing  y±  in.  and 
loosen  the  outer  rear  landing  wire  ^  in.  after  the 
angle  of  incidence  and  stagger  have  been  adjusted 
so  that  corresponding  wires  on  the  right  and  left 
wings  are  the  same  length. 

9.  Tightening    and    Safetying    All    Wires. — (a) 
After  the  wing  is  drooped,  all  flying  wires  should 
be  tightened  to  the  same  tension,  and  just  taut 
enough  to  take  out  all  sag. 

(6)  Next  tighten  all  drift  or  cross  wires  between 
the  front  and  rear  struts  to  the  same  tension. 

(c)  Drift  wires  from  the  wings  to  the  fuselage,  and 
from  the  wings  to  the  landing  gear,  if  any,  should 
be  tightened  last. 

(d)  Safety  all  turnbuckles.     A  wire  too  loose  will 
vibrate  when  the  machine  is  in  the  air. 

The  flying  and  drift  wires  should  be  so  tightened 
that  when  they  take  the  weight  of  the  machine 
in  the  air,  there  will  be  no  sag  in  the  landing 
wires. 

10.  Length  of  Struts,  Positions  of  Fittings,  Warp 
in  Planes. — The  above  instructions  are  given  for 
machines  that  are  true,  that  is,  machines  having 
no  bends,  warps,  or  bows  in  the  spars  and  leading 
or  trailing  edges. 

(a)  Similar  struts  should  be  of  the  same  length. 

(6)  Similar  fittings  occupying  similar  positions 
should  be  spaced  the  same.  If  difficulties  are 
encountered  in  getting  the  measurements  to  tally, 
check  up  the  lengths  of  the  struts  and  the  positions 
of  the  fittings. 


ERECTING  AIRPLANES  149 

(c)  If  the  planes  of  a  machine  are  warped,  the 
machine  should  be  so  aligned  that  the  warp  is 
equally  divided  between  both  planes. 

11.  Alignment  of  Ailerons. — Before  aligning  aile- 
rons, place  the  shoulder  yoke  or  wheel  controlling 
the  ailerons  in  the  center  of  its  path  of  movement. 

(a)  Trailing-edge  Ailerons. — Trailing-edge  ailerons 
should  be  set  ^  inch  lower  than  the  trailing  edge  of 
the  plane  to  which  they  are  attached. 

(6)  Interplane  Ailerons. — Interplane  ailerons 
should  be  set  so  that  they  are  both  in  the  same 
plane,  when  in  neutral  position. 

In  machines  having  interplane  ailerons,  nose 
heaviness  and  tail  heaviness  may  be  corrected  by 
setting  the  trailing  edges  of  the  ailerons  up  or  down. 

The  proper  amount  to  raise  or  lower  the  trailing 
edges  can  be  determined  only  by  experimenting 
with  each  particular  type  of  machine. 

(c)  The  control  wires  should  be  just  tight  enough 
to  eliminate  any  lost  motion. 

12.  Alignment  of  Stabilizer. — Support  the  weight 
of  the  tail  on  the  tail  skid. 

The  rear  edge  of  the  stabilizer  should  be  perfectly 
straight,  and  should  be  parallel  with  lateral  axis  of 
the  machine. 

Stand  behind  the  center  of  the  stabilizer,  and 
align  its  rear  edge  on  the  leading  edge  of  the 
upper  plane  by  sighting.  Tighten  wires  and  safety 
turnbuckles. 

13.  Alignment  of  Elevator  Flaps. — Set  the  ele- 
vator control  in  its  mid-position.     Adjust  the  ele- 


150  MANUAL  OF  AVIATION  PRACTICE 

vator  control  wires  until  the  flaps  are  in  their 
neutral  position  and  both  are  in  the  same  plane. 
The  wires  should  be  just  tight  enough  to  eliminate 
any  lost  motion.  Safety  turnbuckles. 

14.  Alignment  of  Rudder. — Set  the  rudder  con- 
trol (wheel,  foot  pedals,  or  foot  bar)  in  its  mid- 
position.     Adjust  the  rudder  control  wires  until  the 
rudder  is  in  its  neutral  position.     The  control  wires 
should  be  just  tight  enough  to  eliminate  any  lost 
motion.     Safety  the  turnbuckles. 

15.  General. — All  connections  having  been  made, 
carefully  go  over  each  shackle,  pin,  and  turnbuckle, 
and  see  that  all  pins  are  properly  in  place,   all 
nuts  on  bolts  tight  and  all  cotter-pinned..    Try  out 
all  controls  for  action  and  freedom  of  movement. 
See  that  no  brace  wires  are  slack,  yet  not  so  taut 
that  when  plucked  they  "sing." 

16.  Overall  Adjustments. — As  a  final  check,  the 
following   overall   measurements   should   be  taken 
(see  Fig.  39). 

The  straight  lines  AC  and  BC  should  be  equal 
to  within  >£  in.  The  point  C  is  the  center  of  the 
propeller,  or  in  the  case  of  the  pusher  the  center  of 
the  nacelle.  A  and  B  are  points  on  the  main  spar 
and  must  be  at  the  same  distance  from  the  butt  of  • 
the  spar.  They  must  not  be  merely  the  sockets  of 
the  outer  struts  as  these  may  not  be  accurately 
placed.  AC  and  BC  must  be  taken  from  both  top 
and  bottom  spars;  two  measurements  on  each  side 
of  the  airplane. 

Similarly  FD  and  FE  should  be  equal  to  within 


ERECTING  AIRPLANES  151 

>g  in.  F  is  the  center  of  the  fuselage  or  rudder 
post.  D  and  E  are  points  marked  on  both  top  and 
bottom  rear  spars  just  as  A  and  B  were  marked  on 
front  spars. 

If  these  measurements  are  not  correct,  it  is  prob- 
ably due  to  some  of  the  drift  or  antidrift  wires  being 
too  tight  or  too  slack.  These  must  then  be  located 
and  corrected. 

WING  COVERING  AND  PATCHING 

The  wings  are  covered  with  best  quality  Irish 
linen  which  must  have  a  tensile  strength  of  at  least 
50  Ib.  per  inch  width,  undoped,  and  70  Ib.  when 
doped. 

The  linen  strips  are  sewed  together  on  a  sewing 
machine  in  such  a  way  that  when  folded  together 
they  form  a  sort  of  bag  which  just  slips  over  the 
wing  frame.  The  seams  then  run  diagonally  across 
the  wing.  The  bag  is  stretched  up  loosely  and 
tacked  temporarily  along  the  leading  edge.  The 
edges  are  folded  under  a  little  and  sewed  together 
along  the  leading  edge  of  the  wing  and  the  tem- 
porary tacks  are  removed.  To  hold  the  covering 
up  to  the  ribs,  thread  is  looped  through  from  one 
side  of  the  panel  to  the  other  around  the  ribs. 
The  rough  surfaces  made  by  the  thread  along  the 
ribs  and  the  edges  are  covered  over  with  strips  of 
linen  pasted  on  with  dope.  To  make  a  smooth 
job,  the  edges  of  these  strips  are  frayed  out  %  in. 

Three  or  more  coats  of  dope  are  applied  and 
rubbed  down  after  each  coating  is  dry.  This  is 
11 


152  MANUAL  OF  AVIATION  PRACTICE 

then  covered  over  with  one  or  two  coats  of  varnish 
to  make  it  more  weatherproof  and  smooth.  Varnish 
also  prevents  the  dope  from  peeling  off. 

Dope  shrinks  the  linen  and  makes  it  fit  up  tight 
to  the  framework. 

Breaks  in  the  fabric  are  patched  by  first  removing 
the  dope  around  the  break  with  dope  remover 
and  then  sticking  on  a  patch  with  dope.  This  is 
applied  with  a  rag  instead  of  a  brush  in  order  to 
prevent  the  patch  from  becoming  white.  Ten  to 
sixteen  coats  of  dope  are  then  applied  over  the 
patch,  each  coat  being  allowed  to  dry  before  the 
next  is  applied. 

FAULTS   IN  FLIGHT,    DUE   TO    IMPROPER  ALIGNMENT 
AND  HOW  TO  CORRECT  THEM 

An  airplane  pilot  may  experience  difficulty  with 
the  flying  qualities  of  his  machine.  Consequently 
he  should  know  something  about  the  conditions 
which  are  responsible  for  the  various  kinds  of  un- 
satisfactory flying  qualities  which  are  more  or  less 
characteristic  of  airplanes. 

In  the  chapter  on  "Principles  of  Flight"  the 
reader  has  been  made  acquainted  with  such  terms 
as  stability,  instability,  longitudinal  stability,  etc. 
For  the  purposes  of  rigging,  however,  it  will  be  well 
to  review  these  terms  again. 

Stability  is  a  condition  whereby  an  object  dis- 
turbed has  a  natural  tendency  to  return  to  its 
first  and  normal  position.  Example:  a  weight  sus- 
pended by  a  cord. 


ERECTING  AIRPLANES  153 

Instability  is  a  condition  whereby  an  object  dis- 
turbed has  a  natural  tendency  to  move  as  far  as 
possible  away  from  its  first  position,  with  no  tend- 
ency to  return.  Example:  a  stick  balanced  verti- 
cally on  your  finger. 

Neutral  stability  is  a  condition  whereby  an 
object  disturbed  has  no  tendency  to  move  farther 
than  displaced  by  the  force  of  the  disturbance, 
and  no  tendency  to  return  to  its  first  position. 

Now  in  order  that  an  airplane  may  be  reasonably 
controllable,  it  is  necessary  for  it  to  possess  some 
degree  of  stability  longitudinally,  laterally  and 
indirectionally. 

Longitudinal  stability  is  its  stability  about  an 
axis  transverse  to  the  direction  of  normal  hori- 
zontal flight,  and  without  which  it  would  pitch  and 
toss. 

Lateral  stability  is  its  stability  about  its  longi- 
tudinal axis,  and  without  which  it  would  roll  side- 
ways. 

Directional  stability  is  its  stability  about  its  verti- 
cal axis,  and  without  which  it  would  have  no  tend- 
ency to  keep  its  course. 

Whenever  an  airplane  does  not  fly  properly, 
aside  from  conditions  arising  from  engine  or  pro- 
peller trouble,  either  its  longitudinal,  lateral,  or 
directional  stability  is  affected.  When  its  longi- 
tudinal stability  is  affected  we  call  this  condition 
longitudinal  instability;  likewise,  regarding  lateral 
stability  and  directional  stability,  referring  to  these 
conditions  respectively  as  lateral  and  as  directional 


154  MANUAL  OF  AVIATION  PRACTICE 

instability.      The  effect  of  alignment  errors  will  be 
treated  under  the  foregoing  respective  heads. 

Alignment  Errors,  Longitudinal. — 

1.  The  Stagger  May  Be  Wrong. — The  top   sur- 
face or  wing  may  have  drifted  back  a  little  owing 
to  some  of  the  wires,  probably  the  incidence  wires, 
having  elongated  their  loops  or  having  pulled  the 
fittings  into  the  wood.     If  the  top  surface  is  not 
staggered  forward  to  the  correct  amount,  then  con- 
sequently the  whole  of  its  lift  is  too  far  back,  and 
it  will  then  have  a  tendency  to  lift  up  the  tail  of 
the  machine  too  much.     The  airplane  will  then  be 
said  to  be  nose-heavy.     A  }^-in.  error  in  the  stagger 
will  make  a  very  considerable   difference  in  the 
longitudinal  stability. 

2.  The  Angle  at  Which  the  Main  Surfaces  Are 
Set  Relative  to  the  Fuselage  May  Be  Wrong. — This 
will  have  a  bad  effect  especially  in  the  case  of  an 
airplane  with  a  lifting  tail  plane  or  horizontal  stabil- 
izer.    If  the  angle  of  incidence  is  too  great,  the 
machine  will  have  a  tendency  to  fly  " tail-high." 
If  the  angle  is  too  small  the  airplane  may  have  a 
tendency  to  fly  "tail-down." 

3.  The    Fuselage    May    Have    Become    Warped 
Upward  or  Downward. — This  would  give  the  tail 
plane  or  horizontal  stabilizer  an  incorrect  angle  of 
incidence.     If  it  has  too  much  angle,  it  will  lift  too 
much,  and  the  airplane  will  be  " nose-heavy."     If 
it  has  too  little  angle,  it  will  not  lift  enough  and 
the  airplane  will  be  "  tail-heavy." 


ERECTING  AIRPLANES  155 

4.  The  Tail  Plane  May  Be  Mounted  upon  the 
Fuselage  at  a  Wrong  Angle  of  Incidence. — If  this 
condition  exists,  it  must  be  corrected  by  making  a 
change  at  the  fittings.  If  nose-heavy,  the  tail 
plane  should  be  given  a  smaller  angle  of  incidence. 
If  tail-heavy,  it  should  be  given  a  greater  angle  of 
incidence;  but  care  should  be  taken  not  to  give  it 
too  great  an  angle,  because  the  longitudinal  sta- 
bility entirely  depends  upon  the  tail  plane  being 
set  at  a  smaller  angle  of  incidence  than  is  the  main 
surface,  and  if  that  difference  is  decreased  too  much, 
the  airplane  will  become  uncontrollable  longitudi- 
nally. Sometimes  the  tail  plane  is  mounted  on  the 
airplane  at  the  same  angle  as  the  main  surface, 
but  it  actually  engages  the  air  at  a  lesser  angle, 
owing  to  the  air  being  deflected  downward  by  the 
main  surfaces. 

Alignment  Errors,  Lateral. — The  machine  mani- 
fests a  tendency  to  fly  one  wing  down.  The  reason 
for  such  a  condition  is  a  difference  in  the  lifts  of 
the  right  and  left  wings,  assuming  the  motor  torque 
is  already  taken  care  of  by  washout.  That  may 
be  caused  as  follows: 

1.  The  Angle  of  Incidence  of  One  Wing  May  Be 
Wrong. — If  it  is  too  great,  it  will  produce  more 
lift  than  on  the  other  side  of  the  airplane;  and  if 
too  small,  it  will  produce  less  lift  than  on  the  other 
side — with  the  result,  in  either  case,  the  airplane 
will  try  to  fly  one  wing  down. 

2.  Distorted  Surfaces. — If  some  part  of  the  sur- 
face is  distorted,  the  lift  will  not  be  the  same  on 


156  MANUAL  OF  AVIATION  PRACTICE 

both  sides  of  the  airplane,  which,  of  course,  will 
again  cause  it  to  fly  one  wing  down. 

3.  The  Ailerons  May  Be  Set  Slightly  Wrong  — 
This  may  be  due  to  one  control  cable  being  longer 
than  the  other,  or  one  of  the  aileron  horns  being 
bent  or  twisted.  This  condition  can  easily  be  de- 
tected by  setting  the  aileron  control — in  neutral 
and  checking  up  the  position  of  the  ailerons. 

Alignment  Errors,  Directional. — If  there  is  more 
resistance  on  one  side  of  the  airplane  than  on  the 
other  the  airplane  will,  of  course,  tend  to  turn 
to  the  side  having  the  most  resistance.  This  may 
be  caused  by  the  following  conditions: 

1.  The  Angle  of  Incidence  of  the  Right  and  Left 
Surfaces  May  Be  Unequal. — The  greater  the  angle  of 
incidence,  the  greater  the  resistance.     The  less  the 
angle,  the  less  the  resistance. 

2.  //   the    Alignment    of   the   Fuselage,    Vertical 
Stabilizer,   the  Struts  or  Stream-line  Wires  Is  Not 
Absolutely   Correct. — That   is   to   say,    if   they  are 
turned  a  little  to  the  right  or  left  instead  of  being 
in  line  with  the  direction  of  flight — then  they  will 
act  as  a  rudder  and  cause  the  airplane  to  turn  off 
its  course. 

3.  //  Any  Part  of  the  Surface  Is  Disturbed  It 
Will  Cause  the  Airplane  to  Turn  off  Its  Course. — • 
If,  owing  to  the  leading  edge,   spars,   or  trailing 
edge  becoming  bent,  curvature  is  spoiled,  that  will 
result  in  changing  the  amount  of  resistance  on  one 
side  of  the  airplane,   which  will  then  develop   a 
tendency  to  turn  off  its  course. 


ERECTING  AIRPLANES  157 

Additional  Flight  Defects. — In  addition  to  the 
foregoing  the  following  conditions  may  also  exist 
which  cause  trouble  when  flying  as  well  as  when 
landing: 

Airplane  Climbs  Badly. — Such  a  condition,  apart 
from  engine  or  propeller  trouble,  is  probably  due  to 
excess  resistance  somewhere. 

Flight  Speed  Poor. — This  condition  apart  from 
engine  or  propeller  trouble,  is  probably  due  to 
(1)  distorted  surfaces,  (2)  wrong  angle  of  incidence, 
or  (3)  dirt  or  mud,  resulting  ki  excessive  skin  friction 
and  weight. 

Inefficient  Control. — This  is  probably  due  to  (1) 
wrong  setting  of  the  control  surfaces,  (2)  distortion 
of  control  surfaces,  or  (3)  control  cables  being  badly 
tensioned. 

Will  Not  Taxi  Straight. — If  the  airplane  is  uncon- 
trollable on  the  ground  it  is  probably  due  to  (1) 
alignment  of  the  undercarriage  being  wrong,  (2) 
unequal  tension  of  shock  absorbers,  (3)  tires  un- 
equally inflated,  (4)  axle  bent,  (5)  tight  wheel  and 
axle,  (6)  loose  spokes  causing  wheel  to  wobble. 


CHAPTER  IX 
TRUING  UP  THE  FUSELAGE 

Before  an  airplane  is  assembled  for  the  first  time 
after  leaving  the  factory,  and  especially  after  it  has 
made  its  first  few  "  breaking-in "  flights,  the  fusel- 
age or  basic  framework  should  be  carefully  ex- 
amined and  checked  up.  This  is  done  in  order  to 
determine  whether  or  not  the  fuselage  became  dis- 
torted from  rough  usage  during  shipment  (which  is 
always  likely)  or  from  taking  sets  due  to  the  flying 
stresses  to  which  it  was  subjected  for  the  first  time 
during  the  "breaking-in"  flights.  It  frequently 
happens  that  rough  landings  and  "stunt"  flying 
cause  distortions  of  the  fuselage  frame  and  other 
parts  of  the  airplane  so  that  it  is  very  necessary 
to  make  a  careful  inspection  immediately  after  to 
ascertain  not  only  what  twists,  bows  and  stretching 
of  vital  parts  have  resulted,  but  also  to  detect  fit- 
tings, wires,  etc.,  which  may  have  been  pulled  loose 
or  broken.  The  extreme  importance  of  having  your 
airplane  adjusted  correctly  and  carefully,  and  to 
know  that  it  is  in  the  proper  condition  can  not  be 
reiterated  too  often.  And,  since  the  fuselage  is 
the  foundation  from  which,  so  to  speak,  the  entire 
apparatus  is  built  up,  it  is  doubly  important  that 
it  should  always  be  in  correct  adjustment. 

158 


TRUING  UP  THE  FUSELAGE  159 

When  the  fuselage  is  built  in  the  factory  it  is 
placed  on  a  long  table  whose  surface  is  perfectly 
horizontal  and  which  has  metal  strips  inlaid.  This 
table  in  reality  is  a  big  face  plate  especially  arranged, 
as  described,  for  fuselage  truing  in  the  factory. 
The  fuselage,  of  course,  has  had  none  of  its  cover- 
ings applied  when  it  is  placed  on  the  table,  nor  are 
the  accessories  such  as  controls  and  engine  in  place. 
On  this  table  then  the  builders  begin  to  do  the  neces- 
sary adjusting  and  this  is  no  simple  or  quick  job. 
Working  from  a  perfectly  smooth  horizontal  surface 
it  is,  of  course,  easy  to  detect  warpings,  twists,  etc., 
of  the  framework.  These  are  first  remedied  by 
tightening  or  loosening  of  cross  wires,  etc.,  as  the 
case  may  be.  Then,  when  the  fuselage  is  reason- 
ably square  and  level,  lengthwise  and  crosswise, 
as  determined  by  the  eye,  check  measurements  are 
taken  by  rule,  trams  and  level  and  final  adjustments 
made  to  bring  the  various  parts  in  final  proper  rela- 
tion to  one  another.  For  instance,  the  rudder  post 
must  be  perfectly  vertical,  as  determined  by  a 
plumb  line,  when  the  engine  bearers  or  the  top 
longerons  are  level.  The  various  fittings  such  as 
those  for  horizontal  and  vertical  stabilizers  and  the 
engine  sections  and  side  panels  must  all  conform 
accurately  to  one  another  so  that  the  airplane  as  a 
whole,  when  it  is  assembled,  will  not  contain  any 
inherent  defects  such  as  tail  planes  with  slightly 
distorted  angles  of  incidence,  left  main  panels  ahead 
of  right  or  over  or  under  right  main  panels,  fittings 


160  MANUAL  OF  AVIATION  PRACTICE 

so  located  that  an  initial  strain  must  be  imposed 
upon  them  by  forcing  them  together,  etc. 

After  the  fuselage  has  been  lined  up  in  the  factory 
as  described  briefly  above,  it  is  permitted  to  set 
for  a  week  or  so  and  then  it  is  checked  up  again  and 
such  additional  slight  corrections  made  which  would 
be  necessitated  by  the  sets  which  had  occurred. 
The  additional  fittings  required  are  then  applied 
and  the  fuselage  finally  covered  and  sent  away  to 
have  the  engine  and  instruments  applied. 

When  checking  and  truing  a  fuselage  on  the 
flying  field  after  the  airplane  has  been  assembled 
and  flown  the  process  is  not  quite  so  simple  as  when 
the  fuselage  is  checked  up  and  trued  in  the  factory, 
largely  owing  to  the  lack  of  ideal  factory  facili- 
ties and  also  because  so  many  fittings,  coverings, 
etc.,  are  in  the  way  which  one  must  always  be 
cautious  about  removing.  In  general,  the  method 
of  procedure  may  be  outlined  as  follows,  but  it 
must  be  obvious  that  one  can  not  in  a  series  of  writ- 
ten notes  touch  upon  all  the  possible  queries  and 
combinations  of  fuselage  distortions  which  may 
occur  and  the  ways  for  detecting  and  correcting 
them.  A  certain  amount  of  experience  in  the  field 
accompanied  with  some  fixed  habits  of  inspection, 
and  everlasting  curiosity  about  the  perfections  of 
your  machine,  and  a  willingness  and  readiness  al- 
ways to  pitch  in  and  help  correct  the  defects  found, 
will  soon  develop  in  you  the  ability  to  diagnose 
easily  and  quickly  and  remedy  intelligently  what- 
ever trouble  you  may  run  across. 


TRUING  UP  THE  FUSELAGE  161 

For  satisfactory  fuselage  checking  and  truing  let 
us  say  in  the  field  shop,  a  certain  minimum  equip- 
ment of  tools  is  necessary.  This  equipment  is: 

At  least  two  sawhorses  about  3  to  4  ft.  high  for  mounting 
the  fuselage  in  flying  position. 

Several  wooden  wedges  (show  taper)  for  easy  adjustment  of 
fuselage  for  cross  and  lengthwise  level. 

About  25  yd.  of  strong  linen  line  for  checking  center  lines. 

2  carpenter  levels  about  2  to  3  ft.  long. 

4  perfectly  formed  steel  cubes  about  \y±  to  1>£  in.  in  size. 

1  plumb  bob. 

1  small  screw  jack. 

1  pair  of  wood  clamps. 

1  straight  edge  about  12  ft.  long. 

Several  small  Crescent  adjustable  wrenches. 

Several  pliers  with  wire-cutting  attachment. 

Pins  for  manipulating  turnbuckles. 

1  steel  tape. 

1  foot  rule,  6  ft.  long. 

1  small  brass  hammer. 

A  small  work  bench  equipped  with  a  3-in.  or  4-in.  vise. 

The  fuselage  which  is  to  be  trued  is  mounted  on 
the  horse  with  the  wedges  between  the  top  horse 
rails  and  the  lower  longerons.  These  horses  or 
trestles  should  be  so  arranged  that  about  three- 
fourths  of  the  fuselage  toward  the  tail  sticks  out 
unsupported.  In  this  way  it  will  take,  as  near  as 
possible,  its  normal  flying  position.  It  is  always 
desirable,  in  fact  quite  necessary,  especially  when 
checking  a  fuselage  for  the  first  time,  to  have  the 
airplane's  specifications  as  well  as  a  detailed  draw- 
ing of  the  fuselage  and  an  assembly  of  the  airplane 


162  MANUAL  OF  AVIATION  PRACTICE 

as  a  whole  available.     The  reason  for  this,  of  course, 
is  quite  obvious. 

The  engine  bearers  and  the  top  longerons  are  the 
basic  parts  from  which  the  fuselage  as  a  whole  is 
lined  up.  Consequently  the  first  thing  which  is 
done,  when  inspecting  the  fuselage  for  alignment, 
is  to  test  the  truth  of  these  parts.  This  is  done  by 
sighting  the  top  longerons  lengthwise  to  see  if  they 
are  bowed  downward,  upward,  inward  or  outward. 
As  near  as  possible  the  fuselage  is  made  level  on 
the  trestles.  The  steel  blocks  or  cubes  referred  to 
in  the  tool  list  above  are  placed  on  the  longerons 
and  the  straight  edge  and  level  placed  on  these, 
first  crosswise  and  then  lengthwise.  A  string  is 
stretched  over  the  top  of  the  fuselage  touching  the 
top  cross  braces  and  brought  as  close  as  possible  to 
the  center  of  these  pieces.  This  string  should 
stretch  from  the  rudder  post  as  far  forward  as  pos- 
sible. Then  the  cross  wires  or  diagonal  brace  wires 
are  sighted  to  see  how  close  their  intersections  agree 
with  this  center-line  string.  Furthermore,  the  level 
is  placed  on  the  engine  bearers  and  they  are  tested 
for  cross  level  and  longitudinal  level.  If  the  engine 
is  mounted  in  place,  but  one  point  on  the  bearers  will 
be  available  for  this  purpose,  but  the  check  should 
nevertheless  be  made.  It  may  also  be  found  that 
the  longitudinal  level  of  the  engine  bearers  can  be 
tested  from  underneath  by  placing  the  steel  cubes 
mentioned  above  on  the  top  of  the  level  and  then 
holding  the  level  up  against  the  bottom  of  the 
bearers.  As  a  rule,  if  the  fuselage  is  warped  it 


TRUING  UP  THE  FUSELAGE  163 

should  be  possible  to  detect  this  with  the  eye,  but 
when  engine  bearers  are  out  of  line  this  can  only 
be  detected  with  certainty  by  the  use  of  the  level. 

Let  it  be  assumed  that  the  fuselage  is  out  of  true. 
The  first  parts  to  tackle  are,  of  course,  the  engine 
bearers.  If  they  should  not  be  in  line  they  must 
first  be  brought  so,  and  afterward  kept  in  this  con- 
dition. The  diagonal  wires  at  the  front  of  the  fusel- 
age should  be  adjusted  to  make  this  correction.  If 
the  bearers  are  badly  out  of  line  it  will,  perhaps,  be 
wisest  to  remove  the  engine,  or  at  least  loosen  it 
up  from  the  bearers  before  doing  any  adjusting  for 
the  reason  that  it  may  become  strained  by  serious 
pulling  on  the  bearers.  After  the  bearers  are  in 
place,  it  will  be  safe  to  bolt  the  engine  fast  again. 

With  the  engine  bearers  temporarily  disposed  of, 
the  fuselage  proper  is  tackled.  Here  the  first  thing 
to  do  is  to  get  the  top  surfaces  of  the  longerons  level 
crosswise.  Use  the  spirit  level  and  the  two  steel 
cubes  mentioned  in  the  tool  list  for  this  purpose. 
Start  at  the  front  of  the  fuselage  in  the  cock  pit. 
Adjust  the  internal  diagonal  wires  until  the  level 
bubble  is  in  its  proper  place.  Then  measure  these 
first  twTo  sets  of  diagonal  wires,  getting  them  of 
equal  length.  Continue  this  process  throughout  the 
length  of  the  fuselage  until  the  rear  end  is  reached, 
always  working  from  the  front. 

Lastly,  before  proceeding  to  the  next  operation,  try 
the  engine  bearers  for  level  again.  If  out,  make  the 
proper  adjustments. 

If  the  centers  of  the  crosswise  struts  are  not 


164  MANUAL  OF  AVIATION  PRACTICE 

marked,  this  should  first  be  done  before  going 
further.  Then  stretch  a  string  from  No.  1  strut, 
or  as  far  forward  as  possible  to  the  center  of  the 
rudder  post.  All  center  points  on  the  cross  struts, 
if  the  fuselage  is  true  lengthwise,  should  lie  exactly 
on  this  string.  If  not,  adjust  the  horizontal 
diagonal  wires,  top  and  bottom,  working  from  the 
front,  until  the  center-line  points  all  agree.  Always 
check  by  measuring  diagonal  wires  which  are  mates. 
These  should  be  of  equal  length.  If  not,  some  wire 
in  the  series  may  be  overstressed.  In  order  to  pull 
the  center  points  on  the  cross  struts  over,  always 
stop  to  analyze  the  situation  carefully,  determining 
which  are  the  long  diagonals  and  which  the  short 
ones  from  the  way  the  fuselage  is  bowed.  Then 
shorten  the  long  ones  and  ease  off  on  the  short  ones, 
being  careful  never  to  overstress  any  of  the  wires. 

The  last  thing  to  do  is  to  bring  the  longerons  or 
the  center  line  of  the  fuselage  into  level  lengthwise. 
For  this  purpose  a  long  straight-edge,  the  two  cubes, 
and  a  spirit  level  are  of  advantage,  although  simply 
stretching  a  string  closely  over  the  top  of  the 
longeron  may  suffice.  Then  as  in  the  case  of  re- 
moving a  crosswise  bow  in  the  fuselage,  here  too, 
we  manipulate  the  outside  up  and  down  diagonal 
wires  in  bringing  the  top  longerons  into  their  proper 
level  position  lengthwise,  always  working  from  the 
front. 

After  all  this  is  done  it  is  well  to  make  some  overall 
checks  with  steel  tape  or  trams  to  see  how  various 
fittings  located  according  to  the  drawings,  agree 


TRUING  UP  THE  FUSELAGE  165 

with  one  another.  Since  there  is  a  right  and  a 
left  side,  distance  between  fittings  on  these  sides 
may  be  compared.  And,  finally,  the  engine  bearers 
should  be  tried  again.  In  short  no  opportunity 
should  be  neglected  to  prove  the  truth  of  the  fusel- 
age as  a  whole  and  in  detail. 

It  might  be  pointed  out  that  an  excellent  time 
to  check  the  fuselage  is  when  engine  is  being  re- 
moved or  changed.  In  fact  this  time  in  general  is  a 
good  one  to  give  the  airplane  as  a  whole,  a  careful 
inspection. 

After  all  the  necessary  corrections  have  been 
made  and  all  the  parts  of  the  fuselage  brought  into 
correct  relation  with  one  another,  the  turnbuckles 
are  safety  wired  and  then  served  with  tape  to  act 
as  a  final  protection.  The  linen  covering  is  reap- 
plied  if  it  had  previously  to  be  removed  and  the 
level,  empennage  wires,  panels,  etc.,  are  placed  in 
position  and  aligned  as  pointed  out  in  the  notes  on 
assembly  and  alignment. 


CHAPTER  X 

HANDLING   OF  AIRPLANES   IN   THE   FIELD 

AND   AT   THE   BASES    PREVIOUS 

TO  AND  AFTER  FLIGHTS 

No  unimportant  part  of  the  operation  and  main- 
tenance of  airplanes  is  their  handling  in  the  field, 
and  at  the  various  bases  previous  to,  between, 
and  after  flights.  This  phase  of  the  entire  subject 
contemplates  the  transportation  of  airplanes  in 
knockdown  condition  either  by  railway  or  truck, 
their  unloading  and  unpacking,  to  a  certain  extent 
their  assembly,  their  storage  in  hangars  and  sheds, 
their  storage  and  disposition  in  the  open,  their  dis- 
assembling and  packing  for  transportation,  etc. 

The  Unloading  and  Unpacking  of  Airplanes. — 
The  personnel  required  to  unload  an  airplane  prop- 
erly boxed  and  crated  from  a  railway  car,  is  15 
men  and  two  non-commissioned  officers.  The 
tools  needed  for  this  purpose  are: 

lax. 

2  crowbars. 

6  lengths  of  iron  pipe  about  2  in.  in  diameter,  3  ft.  long. 
6  lengths  of  iron  pipe  about  2  in.  in  diameter,  4  ft.  long. 
100  ft.  manila  rope,  1  in.  in  diameter. 

A  regular  flat-bed  moving  truck  or  ordinary  truck 
with  a  flat-bed  trailer  should  be  provided  for  han- 

166 


HANDLING  OF  AIRPLANES  167 

dling  the  machine  from  the  car  to  the  field  erecting 
shop. 

Airplanes  are  usually  shipped  in  automobile  cars 
with  end  doors  or  gondola  cars.  After  opening 
doors  of  cars,  examine  and  inspect  all  crates  and 
boxes  carefully  to  see  that  they  are  all  there  in 
accordance  with  the  bill  of  loading  or  shipping 
memorandum,  as  well  as  to  see  that  they  are 
in  good  condition.  If  any  boxes  are  found 
damaged,  they  should  not  be  removed  from  the 
car  without  first  reporting  the  fact  to  the  receiving 
officer. 

Next,  all  cleats  and  bracing  should  be  removed. 
The  crate  containing  the  fuselage  and  engine  should, 
if  possible,  be  unloaded  first.  The  heavy  end  where 
the  engine  is  fixed  should  be  lifted  up,  have  2-in. 
pipe  rollers  put  underneath  and  manipulated  into 
the  truck  which  has  been  backed  up  against  the 
car  door  so  that  this  heavy  end,  when  finally  placed, 
will  rest  on  the  body  of  the  truck  as  far  forward  as 
possible.  Next  lash  the  front  end  of  the  box 
securely  to  the  truck. 

Should  it  happen  that  the  fuselage  crate  is  so 
located  in  the  car  that  the  light  end  must  of 
necessity  emerge  first  through  the  door,  then  this 
end  may  be  run  on  to  a  truck  and  the  crate  removed 
from  the  car  with  the  heavy  end  adequately  sup- 
ported by  sufficient  help.  Another  truck  is  then 
backed  up  against  the  rear  of  the  first  one  which 
has  been  moved  into  the  clear,  and  the  heavy  end 
of  the  fuselage  crate  brought  to  rest  as  far  forward 


168  MANUAL  OF  AVIATION  PRACTICE 

as  possible  in  the  second  truck.  It  is  then  secured 
and  the  first  truck  released. 

After  the  box  is  properly  lashed  by  means  of  the 
manila  rope,  a  man  should  be  placed  on  each  side 
of  it  to  watch  and  see  that  the  lashings  do  not  loosen 
and  the  box  shift  in  transit.  Trucks  should  be 
driven  slowly,  especially  over  rough  ground,  tracks, 
etc.  In  addition  to  the  fuselage  crate  it  may  also 
be  possible  to  load  the  panel  crates  on  this  same 
truck,  but  as  a  rule  it  is  better  to  load  these  on  a 
second  truck.  Common  sense  goes  a  long  way  in 
transporting  aircrafts  by  motor  trucks. 

Unloading  of  the  crates  is  done  with  the  use  of 
skids  applied  to  the  rear  of  the  truck  and  secured  so 
as  to  form  a  sort  of  an  inclined  plane  down  which  to 
slide  the  boxes  on  the  pipe  rollers  to  the  ground. 
These  skids  should  be  at  least  4  in.  by  4  in.  by  6  ft. 
and  made  of  strong  wood.  The  rear  end  of  the 
crate  may  be  brought  to  the  ground,  rested  there, 
and  the  truck  moved  forward  slowly  until  the  entire 
length  rests  on  the  ground.  Care  must  be  used  not 
to  jolt  or  drop  this  box  at  any  stage  whatsoever. 

When  uncrating  the  fuselage,  remove  the  top  and 
both  ends  of  the  box.  Fold  both  sides  of  box  flat 
down  on  ground  and  use  same  for  assembling 
machine.  The  wing  boxes  should  have  the  tops 
removed  and  planes  lifted  out  in  that  manner. 

Next,  the  airplane  is  assembled  in  accordance 
with  instructions  already  given. 

The  Dismantling  and  Loading  of  Airplanes. — 
When  airplanes  are  to  be  prepared  for  shipment  by 


HANDLING  OF  AIRPLANES  169 

motor  truck  or  railway,  they  should,  of  course,  be 
taken  down  and  crated  similar  to  the  way  they 
were  shipped  from  the  factory.  The  order  in  which 
this  is  done  should  be  as  follows: 

Remove  propeller. 
Unfasten  control  wires. 

Unfasten  main  planes  from  fuselage  and  dismantle  on  ground. 
Remove  tail  surfaces. 

Unless  machine  is  to  be  placed  in  box,  landing  gear  and  tail 
skid  should  remain  attached  to  fuselage. 

If  the  machine  is  crated  it  should  be  handled 
when  shipped  the  same  as  described  above.  If, 
however,  it  is  to  be  loaded  without  being  crated, 
then  the  following  procedure  should  be  observed. 
Using  two  planks,  2  in.  by  12  in.  by  18  ft.  long  for 
runway  from  ground  into  car,  load  machine  into 
car,  engine  first.  Block  wheels  to  prevent  machine 
shifting.  Secure  fuselage,  tail  end,  to  the  floor  of 
the  car  by  means  of  ropes  passed  over  the  fuselage 
and  fastened  to  the  floor  with  cleats.  The  wings 
should  be  crated  against  the  sides  of  car  and  secured 
by  wires,  ropes  or  canvas  strips.  All  boxes  should 
be  marked  with  name  of  organization,  destination, 
weight,  cubic  contents,  hoisting  centers,  number  of 
box,  "This  Side  Up,"  etc.  A  shipping  memo- 
randum should  always  be  made  out  and  mailed  to 
destination  when  shipment  goes  forth. 

Storing  of  Airplanes  and  Parts  at  Bases  and  in 
Fields. — Airplanes  when  not  in  active  flying  duty 
are  stored  in  hangars  or  sheds  especially  adapted 
to  house  them.  Under  certain  conditions  it  is 


170  MANUAL  OF  AVIATION  PRACTICE 

necessary  to  store  them  in  the  open.  In  each  case 
particular  precautions  should  be  observed  in  order 
not  to  subject  the  machines  to  unnecessary  wear 
and  tear. 

Since  moisture  is  one  of  the  airplanes'  worst 
enemies  in  that  it  deteriorates  the  weatherproofing 
and  the  fabric,  distorts  and  otherwise  injures  the 
wooden  parts  of  the  machines  and  worst  of  all, 
rusts  the  metal  parts,  the  first  consideration  for 
proper  storage  facilities  should  be  the  absence  of 
moisture.  Next,  extreme  heat  and  cold  are  a 
menace  to  airplanes.  The  temperature  of  the  air 
surrounding  them  while  in  storage  should  be  regu- 
lated as  much  as  possible.  Under  shelter,  especially 
when  the  machine  is  to  be  out  of  active  service  for 
48  hr.  or  more,  the  entire  machine  should  be  raised 
off  the  ground  a  few  inches  so  that  the  wheels  are 
free  and  the  flexible  connections  released.  This  is 
done  by  the  points  where  the  undercarriage  struts 
meet  the  skids.  Furthermore,  the  wings  might 
well  be  supported  and  the  weight  thus  taken  off 
the  landing  wires,  and  hinge  connections  by  placing 
padded  trestles  underneath  the  wing  skids.  Care 
should  be  exercised  that  dirt,  grease,  water,  etc., 
does  not  accumulate  in  any  part  of  the  airplane. 

Furthermore,  all  water  should  be  drained  from 
the  radiator  and  gasoline  from  the  gasoline  tank. 
The  propeller  should  be  placed  in  a  vertical  posi- 
tion and  covered  with  a  weatherproof  cloth.  The 
engine  cockpit  and  instruments  should  all  be  cov- 
ered and  the  magneto  should  be  enclosed  in  a  thick 


HANDLING  OF  AIRPLANES  171 

layer  of  felt  or  cotton  waste.  If  any  fluid  is  apt 
to  freeze,  and  oil  will  freeze  in  temperatures  low 
enough,  it  should  be  carefully  drained. 

When  spare  parts  such  as  wings,  struts,  fuselages, 
etc.,  are  stored,  the  same  general  precautions  out- 
lined above  should  be  observed.  Spare  planes 
particularly  should  be  placed  in  such  a  manner 
that  their  weight  is  evenly  supported.  Never 
should  planes  of  any  kind  be  laid  flat  on  the  ground. 
They  should  always  stand  edgewise,  with  the  lead- 
ing edge  down,  supported  several  inches  off  the 
ground  on  blocks  or  boards  evenly  spaced.  One 
plane  must  not  be  allowed  to  lean  against  another. 
In  fact,  the  best  way  is  to  suspend  planes  by  means 
of  canvas  slings  hung  from  overhead.  Within  the 
loop  of  the  slings  there  must  be  a  batten  about 
iy%  in.  wide. 

All  parts  of  an  airplane  subject  to  attack  by  rust 
should  be  kept  well  coated  with  grease  or  oil. 
Periodically  the  entire  machine  should  be  wiped 
by  means  of  clean,  dry  cheese  cloth  or  selected 
cotton  waste.  Engines  which  are  in  stored  planes 
or  which  have  been  set  aside  for  future  use  should 
be  turned  over  by  hand  daily. 

It  will  sometimes  be  impossible  for  airplane  sheds 
or  hangars  to  be  brought  up  to  the  front  on  service, 
hence,  airplanes  must  be  prepared  to  remain  in  the 
open.  When  this  is  the  case  they  should  be  placed 
to  the  leeward  of  the  highest  hedge  available,  a 
clump  of  trees,  a  building,  a  bank,  a  knoll,  or  hill, 
etc.  They  should  be  sunk  as  low  as  possible  by 


172  MANUAL  OF  AVIATION  PRACTICE 

digging  a  trench  for  the  wheels  and  undercarriage. 
The  nose  of  the  plane  should,  of  course,  first  be 
run  into  the  wind,  and  then  the  wings  and  the  tail 
pegged  down  with  ropes,  particularly  if  there  is 
any  chance  of  a  wind  starting  up.  The  engine, 
propeller,  instruments,  and  cockpit  should  be  cov- 
ered over  with  a  waterproof  cloth  and  great  care 
taken  to  protect  the  propeller  from  the  sun,  for  it  will 
surely  warp  if  not  cared  for  properly.  At  night 
in  cold  or  wet  weather  the  magneto  should  be  packed 
round  with  waste  and  water  in  the  radiator  drained. 
While  machines  are  stored  in  the  open,  the  neces- 
sity of  wiping  them  to  keep  them  moisture  and  dirt 
free  is  all  the  more  urgent  and  should  be  pursued 
with  doubled  energy. 


CHAPTER  XI 
INSPECTION  OF  AIRPLANES 

Mechanics  in  charge  of  airplanes,  who  are  pri- 
marily responsible  for  their  safety  while  in  their  care, 
should  constantly  think  of  new  methods  for  insuring 
greater  safety  and  reliability.  They  should  in- 
variably bring  any  fresh  points  they  think  of  to 
the  attention  of  their  Flight  Commander,  in  order 
that  the  rest  of  the  Corps  may  benefit  by  them. 
They  should  always  try  to  find  out  the  cause  of 
anything  wrong,  and  inform  the  officer  in  charge 
of  the  machine  of  their  opinion.  They  should  bear 
in  mind  any  particular  incidents  which  may  have 
happened  to  their  machine  while  under  their  charge 
during  each  flight,  and  be  on  the  lookout  for  signs 
of  stresses  that  may  have  occurred  to  the  machine 
in  consequence  of  these  incidents.  For  example,  a 
steep  spiral  may  cause  side  strains  on  the  engine 
bearers;  a  flight  in  bad  weather  may  cause  bending 
stresses  on  the  longitudinal  members  of  the  body, 
besides  stretching  the  landing  and  flying  wires. 
No  part  of  a  machine  can  be  safely  overlooked,  and 
good  mechanics  will  always  be  seeking  for  the  pos- 
sible cause  of  accidents  and  bringing  them  to  the 
notice  of  the  officer  in  charge  of  the  machines. 

173 


174  MANUAL  OF  AVIATION  PRACTICE 

During  all  inspections  the  following  matters  of 
detail  deserve  particular  attention: 

Look  out  for  dirt,  dust,  rust,  mud,  oil  on  fabric. 
Cleanliness  is  the  very  first  consideration. 

Give  the  control  cables  particular  attention. 
These  should  not  be  too  tight,  otherwise  they  will 
rub  stiffly  in  the  guides.  The  hand  should  be  passed 
over  them  to  detect  kinks  and  broken  strands. 
They  should  be  especially  well  examined  where 
they  run  over  pulley.  Don't  forget  the  aileron 
balance  wire  on  the  top  plane. 

See  that  all  wires  are  well  greased  and  oiled,  and 
that  they  are  all  in  the  same  tension.  When 
examining  wires,  be  sure  to  have  machine  on  level 
ground  as  otherwise  it  may  get  twisted,  throwing 
some  wires  into  undue  tension  and  slackening 
others.  The  best  way,  if  time  is  available,  is  to 
jack  the  airplane  up  into  " flying  position."  If  a 
slack  wire  is  found,  do  not  jump  to  the  conclusion 
that  it  must  be  tensioned.  Perhaps  its  opposite 
wire  is  too  tight,  in  which  case  it  should  be  slackened. 

Carefully  examine  all  wires  and  their  connections 
near  the  propeller,  and  be  sure  that  they  are  snaked 
around  with  safety  wire,  so  that  the  latter  may  keep 
them  out  of  the  way  of  the  propeller  if  they  come 
adrift. 

Carefully  examine  all  surfaces,  including  the  con- 
trolling surfaces,  to  see  whether  any  distortions  have 
occurred.  If  distortions  can  be  corrected  by  ad- 
justment of  wires,  well  and  good,  but  if  not,  matter 
should  be  reported. 


INSPECTION  OF  AIRPLANES  175 

Verify  the  angles  of  incidence,  the  dihedral  angle, 
the  stagger,  and  the  overall  measurements  as  often 
as  possible  (at  least  once  a  week)  and  correct  as 
outlined  in  notes  on  assembly  and  adjustment  of 
airplanes. 

Constantly  examine  the  alignment  and  fittings  of 
the  undercarriage,  the  condition  of  tires,  shock 
absorbers  and  the  skids.  Verify  the  rigging  posi- 
tion of  the  ailerons  and  elevators. 

Constantly  inspect  the  locking  arrangements  of 
the  turnbuckles,  bolts,  etc. 

Learn  to  become  an  expert  at  vetting,  which 
means  the  ability  to  judge  the  alignment  of  the 
airplane  and  its  parts  by  eye.  Whenever  you  have 
the  opportunity  practice  sighting  one  strut  against 
another  to  see  that  they  are  parallel.  Standing 
in  front  of  the  machine,  which  in  such  a  case  should 
be  on  level  ground,  sight  the  center  section  plane 
against  the  tail  plane  and  see  that  the  latter  is  in 
line.  Sight  the  leading  edge  against  the  main  spars, 
the  rear  spars,  and  the  trailing  edges,  taking  into 
consideration  the  "washin"  and  " washout."  You 
will  be  able  to  see  the  shadow  of  the  spars  through 
the  fabric.  By  practising  this  sort  of  thing  you 
will,  after  a  time,  become  quite  expert,  and  will  be 
able  to  diagnose  by  eye  faults  in  efficiency,  stability 
and  control. 

The  following  order  should  be  observed  in  the 
daily  and  weekly  inspections : 

Daily  Inspection. — All  struts  and  their  sockets, 
longerons,  skids,  etc. 


176  MANUAL  OF  AVIATION  PRACTICE 

All  outside  wires  and  their  attachments. 

All  control  levers  or  wheels,  control  wires  and  cable 
and  their  attachments. 

All  splices  for  any  signs  of  their  drawing. 

Lift  and  landing  gear  cables  or  wires  for  any  signs 
of  stretching. 

All  fabrics,  whether  on  wings  or  other  parts  of  the 
machine,  for  holes,  cuts,  weak  or  badly  doped 
places,  or  signs  of  being  soaked  with  gasoline,  and 
to  see  if  properly  fastened  to  wings,  etc. 

All  outside  turnbuckles,  to  see  that  they  have 
sufficient  threads  engaged,  and  that  they  are 
properly  locked. 

Axles,  wheels,  shock  absorbers,  and  tires,  pumping 
the  latter  up  to  the  correct  pressure. 

The  seats,  both  for  passenger  and  pilot,  seeing 
that  they  are  fastened  correctly. 

Safety  belts  and  their  fastenings. 

This  examination  should  be  carried  out  systemat- 
ically in  the  following  order: 

(a)  Lower  wings,  landing  gear  complete,  tail 
planes  with  all  wires  attached  to  these  tail  skids 
and  all  attachments  and  rudder. 

(6)  Nacelle  or  fuselage,  bolts  of  lower  plane,  all 
control  levers  and  wires. 

(c)  Top  wings,  wing  flaps  or  ailerons  and  wires. 

Inspection  after  Each  Flight— The  landing  gear, 
tail  skid  and  attachments  and  lift  and  drag  wires  for 
tautness. 

The  wheels,  after  a  rough  landing,  for  bent  spokes, 
uncovering  them  if  necessary. 


INSPECTION  OF  AIRPLANES  177 

After  flying  is  finished  for  the  day,  wipe  all  oil  off  the 
planes  as  far  as  possible  with  a  cloth  or  cotton  waste. 

Weekly  Inspection. — Check  over  all  dimensions, 
span,  chord,  gap,  stagger  of  wings,  angles  of  inci- 
dence or  set  angle  of  wings  and  tail,  dihedral  angle, 
alignment  of  fuselage,  rudder,  elevators,  and  the 
general  truth  of  the  machine. 

Examine  the  points  of  crossing  of  all  wires  to  see 
that  there  are  no  signs  of  wear,  and  that  each  wire 
is  properly  bound  with  insulating  tape  to  prevent 
rubbing. 

Examine  all  places  where  wires  cross  the  strut 
to  see  if  the  plates  require  renewal. 

Examine  any  control  wires  which  are  bound  to- 
gether, and  see  that  they  are  correct.  (Insulating 
tape  should  be  used  for  this  in  preference  to  wires 
which  are  bound  to  slip  and  cause  slack.) 

Examine  the  wheels  for  bent  or  loose  spokes,  un- 
covering if  necessary. 

Examine  all  nuts  and  bolts  of  cotter-pin  applica- 
tions, lock  washers,  etc. 

The  following  directions  for  inspection  are  given 
to  the  U.  S.  Inspectors  of  Airplanes: 

Inspection  of  Cables. 

Are  there  any  kinks  in  the  cable? 

Are  loops  properly  made? 

Are  thimbles  used  in  eyes? 

Are  ends  wrapped  properly  (when  wrapped  splice 
is  used,  wrap  must  be  at  least  fifteen  times  the  di- 
ameter of  wire). 


178  MANUAL  OF  AVIATION  PRACTICE 

No  splicing  of  the  cable  itself  is  permitted. 
Has  acid  struck  cable  during  soldering? 
Are  any  of  the  strands  broken? 
Are  unwrapped  ends  streamlined  and  show  the 
result  of  skilled  workmanship? 

For  Roebling  Hard  Wire. 

Are  there  any  file  cuts  or  flaws  to  weaken  it? 

Is  loop  well  made? 

Is  ferrule  put  on  correctly? 

Are  there  any  sharp  bends  or  kinks? 

Are  wires  too  loose  or  tight  in  machine? 

Fittings. 

Is  workmanship  good? 

Is  material  good? 

Are  holes  drilled  correctly  to  develop  proper 
strength? 

Are  there  any  deep  file  cuts  or  flaws  to  weaken  it  ? 

Is  rivet  or  fastening  wire  put  in  properly? 

Are  thimbles  of  large  enough  diameter? 

Turnbuckles. 

Any  file  cuts,  tool  marks,  or  flaws  in  shank  or 
barrel? 

Are  there  too  many  threads  exposed? 

Is  turnbuckle  of  right  strength  and  size  to  develop 
full  strength  of  wire? 

Are  shanks  bent? 

Are  threads  on  shank  or  in  barrel  well  made? 

Is  barrel  cracked? 

Is  turnbuckle  properly  wired? 


INSPECTION  OF  AIRPLANES  179 

Inspection  of  Linen. 

All  linen  used  in  airplane  construction  should  be 
of  the  following  specifications: 

Free  from  all  knots  or  kinks. 

Without  sizing  or  filling. 

As  near  white  as  possible. 

Weight,  between  3.5  and  4.5  oz.  per  square  yard. 

Strength  as  per  Government  Specifications. 

Inspection  of  Wood. 

All  wood  should  be  inspected  before  varnish  is 
applied. 

Is  grain  satisfactory? 

Are  there  any  sap  or  worm  holes? 

Are  there  any  knots  that  look  as  if  they  would 
weaken  the  member? 

Any  brashiness? 

Any  holes  drilled  for  bolts  or  screws  that  would 
weaken  the  member? 

Any  splits  or  checks? 

Are  laminations  glued  properly? 

Are  there  any  plugged  holes? 

Any  signs  of  dry  rot  ? 


Inspection  of  Metal 

When  fittings  are  copper  plated  and  japanned  the 
inspection  should  take  place  after  the  copper 
plating. 

Have  fittings  been  bent  in  assembling? 

Does  fitting  show  any  defects  that  lessen  its 
strength? 


180  MANUAL  OF  AVIATION  PRACTICE 

Are  holes  drilled  properly.     Do  fittings  fit? 

Sheet  aluminum  should  be  inspected  for  defects 
such  as  cracks,  bad  dents,  etc.  Where  openings 
occur  in  sheet  aluminum  the  corners  should  be 
rounded,  allowing  a  good-sized  radius. 

Directions  for  Work. 

Before  you  start  work  on  rigging  you  are  advised 
as  follows: 

1.  Do  not  hurry  about  the  work.     No  rush  jobs 
can  be  done  in  airplane  rigging. 

2.  You  are  cautioned  against  leaving  tools  of  any 
kind  in  any  part  of  the  airplane. 

3.  The  bolts  and  their  threads  must  not  be  burred 
in  any  way;  for  this  reason,  the  use  of  pliers  or  pipe 
wrenches  on  bolts  is  very  bad  form. 

4.  Start  all  turnbuckles  from  both  ends  every 
time  they  are  connected  up. 

5.  Full  threads  must  be  had  in  every  case  to 
develop  the  full  strength  of  a  bolt  and  nut,  with 
turnbuckles  at  least  turn  on  for  a  distance  equal  to 
three  times  the  thickness  of  the  shank. 

6.  Lock  with  safety  wires  all  turnbuckles  and  pins, 
and  cotter-pin  every  nut. 

7.  Watch  for  kinking  of  wires  and  their  rubbing 
around  controls  and  wherever  they  may  vibrate 
against  one  another. 

8.  All  bolts  and  pins  must  have  an  easy  tapping 
fit  only;  do  not  pound  them  into  position. 


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